U.S. patent application number 12/051497 was filed with the patent office on 2008-10-16 for electrophotographic photoreceptor, process cartridge, and image forming apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Takeshi IWANAGA, Shigeru YAGI.
Application Number | 20080254379 12/051497 |
Document ID | / |
Family ID | 39854025 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080254379 |
Kind Code |
A1 |
IWANAGA; Takeshi ; et
al. |
October 16, 2008 |
ELECTROPHOTOGRAPHIC PHOTORECEPTOR, PROCESS CARTRIDGE, AND IMAGE
FORMING APPARATUS
Abstract
The present invention provides an electrophotographic
photoreceptor, a process cartridge and an image forming apparatus
including the same, wherein the electrophotographic photoreceptor
prevents the generation of excessive residual potential, which
usually occurs on a photoreceptor having a protective layer
composed of an inorganic material, and achieves both of high
durability and favorable electrical characteristics. An
electrophotographic photoreceptor composed of a conductive
substrate having thereon a photosensitive layer and a surface layer
formed in this order, wherein the total composition ratio of a
group 13 element, oxygen, and hydrogen to the total element content
in the surface layer is 0.95 or more, and the abundance ratio of
the oxygen to the group 13 element is from 1.1 to 1.5.
Inventors: |
IWANAGA; Takeshi; (Kanagawa,
JP) ; YAGI; Shigeru; (Kanagawa, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
39854025 |
Appl. No.: |
12/051497 |
Filed: |
March 19, 2008 |
Current U.S.
Class: |
430/66 ;
399/159 |
Current CPC
Class: |
G03G 5/047 20130101;
G03G 5/0525 20130101; G03G 2221/183 20130101; G03G 5/14704
20130101 |
Class at
Publication: |
430/66 ;
399/159 |
International
Class: |
G03G 15/04 20060101
G03G015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 16, 2007 |
JP |
2007-107077 |
Claims
1. An electrophotographic photoreceptor comprising a conductive
substrate having thereon a photosensitive layer and a surface layer
formed in this order, wherein the total composition ratio of a
group 13 element, oxygen, and hydrogen to the total element content
in the surface layer is about 0.95 or more, and the abundance ratio
of the oxygen to the group 13 element is from about 1.1 to about
1.5.
2. The electrophotographic photoreceptor of claim 1, wherein the
abundance ratio of the oxygen to the group 13 element is from about
1.1 to about 1.4.
3. The electrophotographic photoreceptor of claim 1, wherein the
surface layer has a film thickness of from about 0.2 .mu.m to about
2.0 .mu.m.
4. The electrophotographic photoreceptor of claim 1, wherein the
surface layer is formed by plasma CVD.
5. The electrophotographic photoreceptor of claims 3, wherein the
surface layer is formed by plasma CVD.
6. The electrophotographic photoreceptor of claim 1, wherein the
photosensitive layer is an organic photosensitive layer.
7. The electrophotographic photoreceptor of claim 3, wherein the
photosensitive layer is an organic photosensitive layer.
8. The electrophotographic photoreceptor of claim 4, wherein the
photosensitive layer is an organic photosensitive layer.
9. A process cartridge comprising an electrophotographic
photoreceptor, and at least one selected from a charging unit for
charging the surface of the electrophotographic photoreceptor, a
developing unit for developing the electrostatic latent image
formed on the surface of the electrophotographic photoreceptor with
at least a developer containing a toner thereby forming a toner
image, and a transferring unit for transferring the toner image to
a recording medium, wherein the electrophotographic photoreceptor
is the electrophotographic photoreceptor of claim 1, and the
electrophotographic photoreceptor is removable from the main body
of the image forming apparatus.
10. The process cartridge of claim 9, wherein the surface layer of
the electrophotographic photoreceptor has a film thickness of from
about 0.2 .mu.m to about 2.0 .mu.m.
11. The process cartridge of claim 9, wherein the surface layer of
the electrophotographic photoreceptor is formed by plasma CVD.
12. An image forming apparatus comprising an electrophotographic
photoreceptor, a charging unit for charging the surface of the
electrophotographic photoreceptor, an exposure unit for exposing
the surface of the electrophotographic photoreceptor charged by the
charging unit thereby forming an electrostatic latent image, a
developing unit for developing the electrostatic latent image with
a developer containing at least a toner thereby forming a toner
image, and a transferring unit for transferring the toner image to
a recording medium, wherein the electrophotographic photoreceptor
is the electrophotographic photoreceptor of claim 1.
13. The image forming apparatus of claim 12, wherein the surface
layer of the electrophotographic photoreceptor has a film thickness
of from about 0.2 .mu.m to about 2.0 .mu.m.
14. The image forming apparatus of claim 12, wherein the surface
layer of the electrophotographic photoreceptor is formed by plasma
CVD.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2007-107077 filed Apr.
16, 2007.
TECHNICAL FIELD
[0002] The invention relates to an electrophotographic
photoreceptor, a process cartridge, and an image forming
apparatus.
RELATED ART
[0003] Recently, an electrophotography method has been extensively
applied to an image forming apparatus, such as a photocopier or a
printer. Since an electrophotographic photoreceptor (hereinafter,
occasionally referred to as `photoreceptor`) that is used in the
image forming apparatus using the electrophotography method is
exposed to various types of contacts or stresses in the apparatus,
deterioration may occur. Meanwhile, high reliability is required
for digital and color applications of the image forming
apparatus.
[0004] For example, a charging process of photoreceptors has the
following problem. When a photoreceptor is charged under a
non-contact charging system, discharge products adhere to the
photoreceptor, causing image blurring or other problems. Discharge
products attached to the photoreceptor are removed by, for example,
a developer which contains polishing particles and is scraped off
with a cleaning unit. However, in this case, the photoreceptor
surface may be deteriorated by abrasion.
[0005] In recent years, contact charging systems have been widely
used, however abrasion of a photoreceptor may be accelerated also
under these systems.
[0006] Thus, it is desirable for electrophotographic photoreceptors
to have a longer life. In order to increase the life of an
electrophotographic photoreceptor, the photoreceptor must have
higher abrasion resistance, so it is required to have a harder
surface. Although a photoreceptor composed of amorphous silicon has
a hard surface, discharge products tend to adhere to the surface to
cause image blurring or image bleeding, phenomena which are
particularly significant at high humidities.
[0007] In recent years, organic photoreceptors have been widely
used as image holding members of an electrographic image forming
apparatus by virtue of their low cost. However, an organic
photoreceptor has a shorter life than an inorganic photoreceptor
because it is worn by friction with the cleaning blade in contact
with the surface of the photoreceptor.
[0008] In order to solve the above-described problems, it has been
attempted to form a surface protective layer at the surface of a
photoreceptor using a hard film made of diamond like carbon (DLC),
amorphous carbon nitride (CN), or amorphous silicon nitride. In
this way, carbon-based materials are frequently used as the surface
layer of photoreceptors to prevent the occurrence of the
above-described problems.
[0009] As one of the materials composing the protective layer of
the photoreceptor, the inventors have suggested a material
containing a group 13 element and oxygen. An electrophotographic
photoreceptor having a protective layer composed of these materials
is not easily worn down by repeated use, and maintains high water
repellency during repeated use as an electrophotographic
photoreceptor over a long period. Therefore, the
electrophotographic photoreceptor prevents the occurrence of
problems such as deterioration of image quality caused by adhesion
of discharge products.
[0010] In the above-described techniques, the thickness of the
protective layer (surface layer) is preferably larger from the
viewpoint of improving mechanical strength and durability such as
scratch resistance. In particular, if an organic photoreceptor is
arranged below a protective layer having an insufficient thickness,
the protective layer may be significantly deformed due to the soft
underlayer, which results in cracks or other defects on the
protective layer. Accordingly, it is effective to increase the
thickness of the layer.
[0011] On the other hand, in cases where the protective layer is
insulative, increasing the thickness of the protective layer may
adversely affect the electrical characteristics. More specifically,
charges generated upon exposure of a photosensitive layer do not
transmit through the insulative protective layer, and accumulate at
the interface between the protective layer and the photosensitive
layer, and do not recombine with the charges on the surface. The
charges remaining on the surface and the interface between the
protective layer and the photosensitive layer become a residual
potential. The residual potential increases with the increase of
the thickness of the protective layer, which may cause problems
such as a decrease in printed image density following repeated
use.
[0012] In order to prevent such problems, the protective layer of
the surface preferably has electrical conductivity. However, if the
surface protective layer has excessive electrical conductivity, the
electrostatic latent image may bleed in the in-plane direction. In
particular, in cases where the protective layer is composed of the
above-described oxide material, it is difficult to achieve
appropriate electrical conductivity, and problems such as the
bleeding of the electrostatic latent image in the in-plane
direction may occur.
[0013] As described above, a photoreceptor having a surface layer
composed of an inorganic material must have a large thickness to
achieve mechanical durability. However, under present
circumstances, it is difficult to prevent the increase of the
residual potential without deterioration of the image quality.
SUMMARY
[0014] According to an aspect of the invention, there is provided
an electrophotographic photoreceptor comprising a conductive
substrate having thereon a photosensitive layer and a surface layer
formed in this order, wherein the total composition ratio of a
group 13 element, oxygen, and hydrogen to the total element content
in the surface layer is 0.95 or about 0.95 or more, and the
abundance ratio of the oxygen to the group 13 element is from 1.1
or about 1.1 to 1.5 or about 1.5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Exemplary embodiment(s) of the present invention will be
described in detail based on the following figures, wherein:
[0016] FIG. 1 is a schematic cross sectional view showing an
example of the layer structure of the photoreceptor of the present
invention
[0017] FIG. 2 is a schematic cross sectional view showing another
example of the layer structure of the photoreceptor of the
invention.
[0018] FIG. 3 is a schematic cross sectional view showing another
example of the layer structure of the photoreceptor of the
invention.
[0019] FIG. 4 is a schematic view showing an example of the film
forming apparatus used in the invention.
[0020] FIG. 5 is a schematic block diagram showing an example of
the process cartridge and image forming apparatus of the
invention.
DETAILED DESCRIPTION
[0021] Exemplary embodiments of the invention are described in
detail hereinafter.
[0022] The above-described problems are solved by the invention as
described below.
[0023] More specifically, the invention in accordance with a first
aspect of the invention is an electrophotographic photoreceptor
composed of a conductive substrate having thereon a photosensitive
layer and a surface layer formed in this order, wherein the total
composition ratio of a group 13 element, oxygen, and hydrogen to
the total element content in the surface layer is 0.95 or about
0.95 or more, and the abundance ratio of the oxygen to the group 13
element is from 1.1 or about 1.1 to 1.5 or about 1.5.
[0024] The invention in accordance with a second aspect is the
electrophotographic photoreceptor of the first aspect, wherein the
abundance ratio of the oxygen to the group 13 element is from 1.1
or about 1.1 to 1.4 or about 1.4.
[0025] The invention in accordance with a third aspect is the
electrophotographic photoreceptor of the first or second aspect,
wherein the surface layer has a film thickness of from 0.2 .mu.m or
about 0.2 .mu.m to 2.0 .mu.m or about 2.0 .mu.m.
[0026] The invention in accordance with a fourth aspect is the
electrophotographic photoreceptor of any one of the first to third
aspects, wherein the surface layer is formed by plasma CVD.
[0027] The invention in accordance with a fifth aspect is the
electrophotographic photoreceptor of any one of the first to fourth
aspects, wherein the photosensitive layer is an organic
photosensitive layer.
[0028] The invention in accordance with a sixth aspect is a process
cartridge composed of an electrophotographic photoreceptor, and at
least one selected from a charging unit for charging the surface of
the electrophotographic photoreceptor, a developing unit for
developing the electrostatic latent image formed on the surface of
the electrophotographic photoreceptor with at least a developer
containing a toner thereby forming a toner image, and a
transferring unit for transferring the toner image to a recording
medium, wherein the electrophotographic photoreceptor is the
electrophotographic photoreceptor of any one of the first to fifth
aspects, and the electrophotographic photoreceptor is removable
from the main body of the image forming apparatus.
[0029] The invention in accordance with a seventh aspect is an
image forming apparatus composed of an electrophotographic
photoreceptor, a charging unit for charging the surface of the
electrophotographic photoreceptor, an exposure unit for exposing
the surface of the electrophotographic photoreceptor charged by the
charging unit thereby forming an electrostatic latent image, a
developing unit for developing the electrostatic latent image with
a developer containing at least a toner thereby forming a toner
image, and a transferring unit for transferring the toner image to
a recording medium, wherein the electrophotographic photoreceptor
is the electrophotographic photoreceptor of any one of the first to
fifth aspects.
[0030] <Electrophotographic Photoreceptor>
[0031] The electrophotographic photoreceptor of the invention is
composed of a conductive substrate having thereon a photosensitive
layer and a surface layer formed in this order, wherein the total
composition ratio of the group 13 element, oxygen, and hydrogen to
the total element content in the surface layer is 0.95 or about
0.95 or more, and the abundance ratio of the oxygen to the group 13
element is from 1.1 or about 1.1 to 1.5 or about 1.5.
[0032] When the surface layer composed of an inorganic material as
described above is provided as a protective layer on a
photoreceptor, the residual potential of the photoreceptor may
increase. The increase of the residual potential is more
significant when the inorganic thin film has a large thickness. In
some cases, the residual potential may be 100 V or more.
[0033] The electrical conductivity may be increased by changing the
composition of the elements composing the surface layer. For
example, an outermost surface layer of oxidized (or naturally
oxidized) gallium nitride film is stoichiometric gallium oxide and
is insulative, however it is known that oxides composed of oxygen
and a metal element in nonstoichiometric ratio, for example, indium
oxide, gallium oxide, zinc oxide, and lead oxide, develop
electrical conductivity because conduction electrons are generated
by the oxygen deficiency in the structure.
[0034] However, the electrical resistance of the oxides is
significantly decreased by slightly changing the abundance ratio
between oxygen and the metal element, which makes it difficult to
delicately adjust the resistance value to prevent the occurrence of
image defects such as the bleeding of the electrostatic latent
image in the in-plane direction.
[0035] As a result of the study by the inventors, it is found that
the adjustable range of the electrical resistance is broadened and
both of the increase of the residual potential and the occurrence
of image defects are prevented when, for example, the gallium oxide
contains hydrogen, and the abundance ratio of oxygen to gallium is
within a specified range.
[0036] More specifically, it has been found that both of the
electrical characteristics and the image characteristics are
effectively achieved when the total composition ratio of the group
13 element, oxygen, and hydrogen with reference to the surface
layer containing the group 13 element, oxygen, and hydrogen is
about 0.95 or more, and the abundance ratio of the oxygen to the
group 13 element is from about 1.1 to about 1.5.
[0037] In the gallium oxide film containing hydrogen, hydrogen is
considered to combine with gallium thereby electrically
inactivating electrons of gallium deficient in oxygen to influence
the electrical characteristics. In addition, hydrogen contained in
the film is considered to increase flexibility of the bonds. The
relationship between the composition and electrical characteristics
of the gallium oxide containing hydrogen is considered to be
different from that of gallium oxide containing no hydrogen.
However, it is not evident why the controllability of the
electrical resistance is improved by the above-described
composition (structure).
[0038] If the total composition ratio of the elements is less than
about 0.95, for example, a group 15 element such as N, P, or As may
combine with gallium to give unignorable influences. In this case,
the appropriate range of the abundance ratio of oxygen to the group
13 element which achieves both of the electrical characteristics
and the image characteristics defined in the invention cannot be
established.
[0039] The total composition ratio of the 13 element, oxygen, and
hydrogen is preferably 0.99 or about 0.99 or more.
[0040] If the abundance ratio of oxygen to the group 13 element is
less than about 1.1, the electrical resistivity of the film is so
low that the electrostatic latent image bleeds in the in-plane
direction, which results in the failure of achieving the intended
image resolution. If the abundance ratio is more than about 1.5,
the material composed of the group 13 element, oxygen, and hydrogen
becomes unstable.
[0041] The abundance ratio of oxygen to the group 13 is desirably
from 1.1 or about 1.1 to 1.4 or about 1.4, more preferably from 1.1
or about 1.1 to 1.3 or about 1.3. If the abundance ratio is more
than about 1.4, the film has insufficient electrical conductivity,
and the increase of the film thickness may produce a problem of
excessive residual potential.
[0042] The elemental composition in the invention refers to the
value averaged in the film thickness direction of the outermost
surface excluding the range from the surface layer to a depth of 10
nm. The range from the outermost surface to a depth of 10 nm is
excluded to eliminate the influence of contamination by carbon and
others, and the influence of natural oxidation. Even if a
stoichiometric insulating film is formed by the natural oxidation
in the range from the surface to a depth of 10 nm or less, the
electrical characteristics of the photoreceptor are hardly
affected. The elemental composition may be inclined toward the film
thickness direction, wherein the value is averaged in the film
thickness direction.
[0043] Hereunder is a description of the structure of the
electrophotographic photoreceptor of an exemplary embodiment of the
present invention.
[0044] FIG. 1 is a schematic cross-section showing an example of a
layer structure of a photoreceptor of an exemplary embodiment of
the present invention, wherein 1 denotes a conductive substrate, 2
denotes a photosensitive layer, 2A denotes a charge generation
layer, 2B denotes a charge transport layer, and 3 denotes a surface
layer.
[0045] The photoreceptor shown in FIG. 1 has a layer structure
where on the conductive substrate 1 is formed with the charge
generation layer 2A, the charge transport layer 2B, and the surface
layer 3 in this order. The photosensitive layer 2 includes two
layers of the charge generation layer 2A and the charge transport
layer 2B.
[0046] FIG. 2 is a schematic cross-section showing another example
of a layer structure of the photoreceptor of an exemplary
embodiment of the present invention, wherein 4 denotes an under
coating layer, 5 denotes an intermediate layer, and the others are
the same as shown in FIG. 1. The photoreceptor shown in FIG. 2 has
a layer structure where on the conductive substrate 1 is formed
with the under coating layer 4, the charge generation layer 2A, the
charge transport layer 2B, the intermediate layer 5, and the
surface layer 3 in this order.
[0047] FIG. 3 is a schematic cross-section showing another example
of a layer structure of a photoreceptor of an exemplary embodiment
of the present invention, wherein 6 denotes the photosensitive
layer and the others are the same as shown in FIG. 1 and FIG.
2.
[0048] The photoreceptor shown in FIG. 3 has a layer structure
where on the conductive substrate 1 is formed with the
photosensitive layer 6 and the surface layer 3 in this order. The
photosensitive layer 6 is a layer having integrated functions of a
charge generation layer 2A and the charge transport layer 2B shown
in FIG. 1 and FIG. 2.
In the exemplary embodiment of the invention, the photosensitive
layers 2 and 6 may be composed of an organic material or an
inorganic material.
[0049] Specifically, the group 13 element contained in the surface
layer 3 may be at least one selected from Al, Ga and In. Two or
more elements may be contained in the surface layer.
[0050] The content of hydrogen contained in the surface layer 3 is
preferably from 1 atom % to 30 atom %, more preferably from 5 atom
% to 20 atom %. If the content of hydrogen is less than 1 atom %,
the surface layer 3 may have insufficient effect of electrically
inactivating electrons of the group 13 element deficient in oxygen.
If the content is more than 30 atom %, the probability that two or
more hydrogen atoms combine with the group 13 element and a
nitrogen atom increases, so that the three-dimensional structure
may be collapsed to offer insufficient hardness and chemical
stability, in particular water resistance.
[0051] The surface layer 3 in the exemplary embodiment of the
invention is, as described above, composed mainly of oxygen, the
group 13 element, and hydrogen, and may contain other elements as
impurities. However, excessive impurities may affect the electrical
characteristics, so that the amount of impurities is preferably
smaller. Specifically, the amount of impurities is 5 atom % or
less, preferably 1 atom % or less. In particular, in cases where
nitrogen atoms are contained, the content of the nitrogen atoms is
desirably 1 atom % or less.
[0052] The content of elements such as group 13 elements and oxygen
in the surface layer 3 of an exemplary embodiment of the invention
as well as the distribution in the direction of thickness can be
determined as follows by Rutherford back scattering (may be
referred to "RBS" hereinafter).
[0053] An accelerator (trade name: 3SDH PELLETRON, manufactured by
NEC corporation), an end station (trade name: RBS-400, manufactured
by CE & A Co., Ltd.), and a system (trade name: 3S-R10) are
used for RES. The data is analyzed using HYPRA program (trade name,
manufactured by CE & A Co., Ltd.).
[0054] The measuring condition of RBS is He++ ion beam energy of
2.275 eV, detection angle of 160.degree., grazing angle with
respect to incident beam of about 109.degree..
[0055] The RBS measurement is specifically carried out as
follows.
[0056] In the RBS measurement, the He.sup.++ ion beam is incident
orthogonally to the sample, and the detector is set at 160.degree.
with respect to the ion beam, so as to measure signals of He
backscattered. From the detected energy and intensity of He, the
composition ratio and the film thickness are determined. In order
to improve the accuracy of obtaining the composition ratio and the
film thickness, the spectrum may be measured with two detection
angles. The accuracy can be improved by measuring and cross
checking with two different detection angles having different
resolutions in the depth direction and different backscattering
dynamics.
[0057] The number of He atoms backscattered by target atoms is
determined by three factors of; 1) atomic number of the target
atom, 2) energy of the He atoms before scattering, and 3)
scattering angle. The density is assumed by calculation from the
measured composition, and the film thickness is calculated using
this. The error of the density is within 20%.
[0058] Moreover, the hydrogen content can be calculated by Hydrogen
Forward Scattering (hereinafter, may be referred to as HFS) as
shown below.
[0059] For the HFS, an accelerator (trade name: 3SDH PELLETRON,
manufactured by NEC), and an endstation (trade name: RBS-400,
manufactured by CE&A Co., Ltd.) are used, and a 3S-R10 is used
as the system. The HYPRA program of CE & A Co., Ltd. is used
for analysis. The measurement conditions of the HFS are as
follows.
[0060] He.sup.++ Ion Beam Energy: 2.275 eV
[0061] Detection Angle 160.degree.
[0062] Grazing Angle with respect to incident beam 30.degree.
[0063] In the HFS measurement, by setting the detector at
30.degree. with respect to the He.sup.++ ion beam, and the sample
at 75.degree. with respect to the normal line, signals of hydrogen
scattered in front of the sample can be taken. At this time,
preferably the detector is covered with a thin aluminum foil to
remove He atoms scattered together with hydrogen. The amount is
measured by comparing the hydrogen counts of the reference sample
and the target sample after standardization by the stopping power
As the reference sample, an H ion injected Si sample and muscovite
were used. The muscovite is known to have a hydrogen concentration
of about 6.5 atomic %. H adsorbed in the most outer surface can be
measured by subtracting the H amount adsorbed on a clean Si
surface. Other examples include, however not limited to, secondary
ion mass spectrometry (SIMS), X ray photoelectron spectroscopy
(XPS), Auger electron spectroscopy (AES), X-ray fluorescence
elemental analysis (EDS), energy dispersive X-ray fluorescence
analysis (EDX), and electron probe microanalyzer (EPMA), and
electron energy loss spectroscopy (EELS). They may be used alone or
in combination of two or more of them.
[0064] The elemental composition data in the depth direction may be
measured by, for example, a method of profiling the depth from the
surface, a method of measuring the surface with the surface being
etched by sputtering in a vacuum, or a method of mapping the
composition of a sectional sample. The method may be selected in
accordance with the analysis method. Under any method, the
elemental composition in the invention is determined not on the
outermost surface of the surface layer alone but the whole layer
excluding the range from the outermost surface to a depth of 10
nm.
[0065] The thickness of the surface layer 3 in accordance with the
exemplary embodiment of the invention is desirably from 0.2 .mu.m
or about 0.2 .mu.m to 2.0 .mu.m or about 2.0 .mu.m. If the
thickness is less than about 0.2 .mu.m, the layer has insufficient
mechanical strength, which may be result in damages on the
photoreceptor during traveling. For example, stoichiometric gallium
oxide is usually transparent in the visible region. However, the
material in accordance with the exemplary embodiment of the
invention, in which the composition ratio of oxygen to gallium is
from 1.1 or about 1.1 to 1.5 or about 1.5, absorbs light in the
visible region, so that if the thickness is more than about 2.0
.mu.m, the amount of exposure of the photosensitive layer during
formation of the electrostatic latent image may be
insufficient.
[0066] The thickness of the surface layer 3 is more preferably from
0.2 .mu.m or about 0.2 .mu.m to 1.0 .mu.m or about 1.0 .mu.m.
[0067] Each layer of the photoreceptor of an exemplary embodiment
of the present invention will be described in more detail along
with the method for manufacturing the same.
[0068] The layer structure of the photoreceptor of an exemplary
embodiment of the present invention includes a photosensitive layer
and a surface layer formed on a conductive substrate in this order.
The photosensitive layer of an exemplary embodiment of the present
invention may be constructed with organic substances or inorganic
substances. An under-coating layer such as an intermediate layer
may be provided between these layers, if necessary. The
photosensitive layer may include plural layers as described above,
and each layer may have a different function (function separation
type).
[0069] In a case in which the photosensitive layer is constructed
with organic materials, The organic polymer compound included in
the photosensitive layer may be thermoplastic or thermosetting, or
it may be formed by reacting two types of molecules. Moreover,
between the photosensitive layer and the surface layer may be
provided an intermediate layer from the viewpoints of adjusting the
hardness, the coefficient of expansion, and the elasticity,
improving the adhesiveness, and the like. The intermediate layer
may show intermediate characteristics with respect to both of the
physical characteristics of the surface layer and the physical
characteristics of the photosensitive layer (charge transport layer
in the case of the function separation type). Moreover, if the
intermediate layer is provided, the intermediate layer may act as a
layer which traps charges.
[0070] The photosensitive layer may be a function separation type
photosensitive layer 2 having the charge generation layer 2A and
the charge transport layer 2B separately as shown in FIG. 1, or may
be a function integration type photosensitive layer 6 as shown in
FIG. 2. In the case of the function separation type, the surface
side of the photoreceptor may be provided with the charge
generation layer, or the surface side may be provided with the
charge transport layer. A photosensitive layer will be described
below focusing on the function separation type photosensitive layer
2.
[0071] If a surface layer 3 is formed on the photosensitive layer
by a method described later, in order to prevent decomposition of
the photosensitive layer 2 due to the irradiation of
electromagnetic radiation of shorter wavelengths other than heat,
the photosensitive layer surface may be previously provided with a
short-wavelength light absorber layer against ultraviolet light or
the like, prior to formation of the surface layer 3.
[0072] Moreover, the layer containing an ultraviolet absorber (for
example, a layer formed by application or the like of a layer
dispersed in a polymeric resin) may be provided on the
photosensitive layer surface.
[0073] In this manner, prior to formation of the surface layer 3,
the photoreceptor surface is provided with the intermediate layer,
and thereby effects on the photosensitive layer by short-wavelength
light such as ultraviolet light when forming the surface layer 3,
corona discharge if the photoreceptor is used in the image forming
apparatus, or ultraviolet light from other various light sources
may be prevented.
[0074] While the surface layer 3 may be either amorphous or
crystalline, it is preferable that the upper layer of the surface
layer 3 is also amorphous for improving slidability of the surface
of the photoreceptor.
[0075] (Formation of the Surface Layer)
[0076] The method for forming the surface layer 3 will be described
below. The surface layer 3 may be formed directly on the
photosensitive layer so that the group 13 element and nitrogen are
contained. The surface of the photosensitive layer 2 may be cleaned
with plasma. The surface layer may be formed by a generally known
method for forming a thin film. In cases where a surface layer is
formed on an organic photosensitive layer, the temperature of the
organic photoreceptor as the substrate to be coated is preferably
about 150.degree. C. or less. In particular, plasma CVD is
preferable from the viewpoints of, for example, forming an
inorganic thin film in accordance with the exemplary embodiment of
the invention with good adhesiveness on a substrate such as
amorphous silicon or an organic photosensitive layer, forming an
inorganic thin film having a composition range in accordance with
the exemplary embodiment of the invention with good controllability
according to the supply of the raw materials, and capable of
forming a film at low temperatures. Other examples include, but not
limited to, catalytic CVD, vacuum deposition, sputtering, ion
plating, and molecular beam epitaxial growth.
[0077] FIG. 4 schematically illustrates the film forming apparatus
that is used for forming the surface layer for the photoreceptor
according to an exemplary embodiment of the present invention.
[0078] A film forming apparatus 30 includes a vacuum chamber 32 for
vacuum exhaustion.
[0079] In the vacuum chamber 32, a support member 46 is provided to
rotatably support an electrophotographic photoreceptor 50 which is
not subjected to forming the protective layer (hereinafter,
referred to as `non-coated photoreceptor`) so that a longitudinal
axis of the non-coated photoreceptor 50 is identical to a rotation
axis. The support member 46 is connected through a support shaft 52
for supporting the support member 46 to a motor 48, and a driving
force of the motor 48 is capable of being transferred through the
support shaft 52 to the support member 46.
[0080] After the non-coated photoreceptor 50 is supported by the
support member 46, the motor 48 is driven to transfer the driving
force of the motor 48 through the support shaft 52 and the support
member 46 to the non-coated photoreceptor 50, thus rotating the
non-coated photoreceptor 50 while the longitudinal axis is
identical to the rotation axis.
[0081] An exhaust pipe 42 is formed at an end of the vacuum chamber
32 to exhaust gas from the vacuum chamber 32. The exhaust pipe 42
communicates with the vacuum chamber 32 through an opening 42A of
the vacuum chamber 32 at an end thereof, and is connected to a
vacuum exhaust unit 44 at another end thereof. The vacuum exhaust
unit 44 includes one or a plurality of vacuum pumps. However, the
vacuum exhaust unit may include a unit for controlling an exhaust
rate, such as a conductance valve, if necessary.
[0082] When the vacuum exhaust unit 44 is driven so as to discharge
air from the vacuum chamber 32 through the exhaust pipe 42, the
inside of the vacuum chamber 32 is decompressed to a predetermined
pressure (ultimate vacuum). The ultimate vacuum is preferably 1 Pa
or less, more preferably 0.1 Pa or less. In the invention, as
described later, the abundance ratio between oxygen and the group
13 element is controlled by the ratio of the feed rate of the
gallium source and oxygen. If the ultimate vacuum is high, the
amount of oxygen in the reaction atmosphere is greater than the
supply because of the influence of oxygen and water remaining in
the air, which results in poor controllability over the
composition.
[0083] A discharge electrode 54 is provided in the vicinity of the
non-coated photoreceptor 50 disposed in the vacuum chamber 32. The
discharge electrode 54 is electrically connected to a high
frequency electric source 58 via the matching box 56. The high
frequency electric source 58 may be a DC or AC power supply, and
preferably a high frequency AC power supply from the viewpoint of
efficiently exciting gases.
[0084] The discharge electrode 54 has a plate shape, and is
provided so that a longitudinal-axis direction of the discharge
electrode 54 is identical to a rotation-axis direction
(longitudinal-axis direction) of the non-coated photoreceptor 50.
The discharge electrode 54 is spaced from an external
circumferential surface of the non-coated photoreceptor 50. The
discharge electrode 54 has a hollow structure (cave shape), and one
or a plurality of openings 34A in a discharge side thereof to feed
gas for generating plasma. If the discharge electrode 54 does not
have the cave shape and the openings 34A on the discharge side
thereof, the gas for generating the plasma is fed through a gas
inlet that is separately formed, and flows between the non-coated
photoreceptor 50 and the discharge electrode 54. Additionally, in
order to prevent the occurrence of discharge between the discharge
electrode 54 and the vacuum chamber 32, it is preferable that an
earthed member cover an electrode side other than a side facing the
non-coated photoreceptor 50 while a clearance of about 3 mm or less
is left.
[0085] If high frequency power is supplied from the high frequency
electric source 58 through the matching box 56 to the discharge
electrode 54, the discharge is caused by the discharge electrode
54.
[0086] A gas feeding pipe 34 is formed in a region that faces the
non-coated photoreceptor 50 so that the discharge electrode 54 is
provided between the region and the untreated photoreceptor in the
vacuum chamber 32, thus feeding gas through the hollow discharge
electrode 54 to the non-coated photoreceptor 50 in the vacuum
chamber 32.
[0087] The gas feeding pipe 34 communicates with the discharge
electrode 54 at an end thereof (that is, the gas feeding pipe
communicates with the vacuum chamber 32 through the discharge
electrode 54 and the openings 34A), and is connected to a gas
feeder 41A, a gas feeder 41B, and a gas feeder 41C at another end
thereof.
[0088] The gas feeder 41A, the gas feeder 41B, and the gas feeder
41C each include an MFC (mass flow controller) 36 for controlling a
feed rate of the gas, a pressure controller 38, and a gas feeding
source 40. The gas feeding sources 40 of the gas feeder 41A, the
gas feeder 41B, and the gas feeder 41C are connected through the
pressure controllers 38 and the MFCs 36 to another end of the gas
feeding pipe 34.
[0089] While a feeding pressure of the gas is controlled by the
pressure controller 38 and the feeding rate of the gas is
controlled by the MFC 36, the gas is fed from the gas feeding
source 40 through the gas feeding pipe 34, the discharge electrode
54, and the openings 34A to the non-coated photoreceptor 50 of the
vacuum chamber 32.
[0090] Additionally, the types of gases that are charged in the gas
feeding sources 40 provided in the gas feeder 41A, the gas feeder
41B, and the gas feeder 41C may be the same. However, in the case
of when treatment is performed using a plurality of types of gases,
the gas feeding sources 40 where different types of gases are
charged may be used. In this case, different types of gases are fed
from the gas feeding sources 40 of the gas feeder 41A, the gas
feeder 41B, and the gas feeder 41C to the gas feeding pipe 34 to
form a mixture gas, and the mixture gas is fed through the
discharge electrode 54 and the openings 34A to the non-coated
photoreceptor 50 in the vacuum chamber 32.
[0091] Further, raw material gas containing a group 13 element is
also supplied to the non-coated photoreceptor 50 in the vacuum
chamber 32. The raw material gas is introduced from a raw material
gas feeding source 62 into the vacuum chamber 32 via a gas
introduction pipe 64 whose tip is a shower nozzle 64A.
When the group 13 element is gallium, the feed gas may be a
gallium-containing gas compound such as trimethylgallium or
triethylgallium, or metallic gallium. The oxygen source may be
O.sub.2 or an oxygen-containing substance.
[0092] In the example shown in FIG. 4 described is a case where the
discharge system by the discharge electrode 54 is capacitance type.
The discharge system, however, may alternatively be inductance
type.
[0093] The film formation may be conducted, for example, as
follows. The inside of the vacuum chamber 32 is decompressed by the
vacuum exhaust unit 44 to a predetermined pressure. In this state,
high frequency electric power is supplied from the high frequency
electric source 58 to the discharge electrode 54 via the matching
box 56, and a plasma-generating gas is introduced into the vacuum
chamber 32 through the gas feeding pipe 34. At this time, plasma is
generated on the discharge side of the discharge electrode 54 and
is radiated therefrom to the opening 42A of the exhaust pipe
42.
[0094] The pressure in the vacuum chamber 32 during the plasma
generation is preferably from 1 Pa to 500 Pa.
[0095] In the exemplary embodiment of the invention, the
plasma-generating gas contains oxygen. The gas may be a mixed gas
further containing inert gas such as He or Ar, and a
non-film-forming gas such as H.sub.2. The non-film-forming gas and
inert gas may be used to control the pressure and other
characteristics of the reaction atmosphere in the reaction vessel.
In particular, hydrogen is important for the reaction at low
temperatures as described later.
[0096] Next, by introducing gaseous trimethylgallium
(organometallic compound containing a group 13 element) having been
diluted with hydrogen using hydrogen as a carrier gas, into the
vacuum chamber 32 via a gas introduction pipe 64 and a shower
nozzle 64A while causing hydrogen from a gas feeding source 60 to
pass through a raw material gas feeding source 62, it is possible
to cause activated oxygen and trimethylgallium to react in an
atmosphere containing active hydrogen, and thereby forming a film
containing hydrogen, oxygen and gallium in the surface of the
non-coated photoreceptor 50.
[0097] In this exemplary embodiment, it is desirable to form a film
with a compound of a group 13 element and oxygen containing
hydrogen on the non-coated photoreceptor 50 by introducing O.sub.2
gas and H.sub.2 gas as a mixture into the discharge electrode 54
and simultaneously producing active species, thereby decomposing
trimethylgallium gas.
When hydrogen gas and oxygen gas are simultaneously activated in
the plasma, and reacted with an organic metal compound containing
the group 13 element, active hydrogen generated by plasma discharge
may etch the hydrocarbon group such as a methyl group or an ethyl
group contained in the organic metal gas, whereby a film of the
compound containing the group 13 element and oxygen which hardness
of the film formed at a low temperature is equal to that formed at
a high temperature is favorably formed without giving damages to
the surface of an organic matter (organic photosensitive layer) or
the organic matter.
[0098] Specifically, the hydrogen gas concentration in the
plasma-generating gas supplied for the activation is preferably
about 10% by volume or more. If the hydrogen gas concentration is
less than about 10% by volume, etching reaction insufficiently
proceeds even at a low temperature, and an oxide compound of the
group 13 element having a high content of hydrogen is generated,
which may result in the formation of a film having insufficient
water resistance and being unstable in the air.
[0099] In cases where the surface layer 3 is formed by plasma CVD,
the abundance ratio of oxygen to gallium may be controlled by the
supply of the gallium source and oxygen source. In this case, the
molar ratio of the oxygen gas supply to the trimethylgallium (TMGa)
gas supply, or [O.sub.2]/[TMGa] is preferably from 0.1 or about 0.1
to 10 or about 10.
[0100] Under other methods, the growth atmosphere may be controlled
by changing the gas supply, and sputtering may be controlled by the
proportion of gallium and oxygen contained in the target.
[0101] The surface temperature of the non-coated photoreceptor 50
during film formation is not particularly limited, however the
surface temperature of an amorphous silicon photoreceptor is
preferably from 50.degree. C. to 350.degree. C. during film
formation, and that of an organic photoreceptor is preferably from
0.degree. C. to 150.degree. C. Especially, in the case of when the
film is formed on the organic photoreceptor, it is preferable that
the surface temperature of the non-coated photoreceptor 50 be
100.degree. C. or less. In the case of when the surface temperature
is higher than 150.degree. C. due to the plasma even though the
temperature of the untreated photoreceptor 50 is 150.degree. C. or
less, the organic photoreception layer may be damaged by heat.
Thus, it is preferable to set the temperature of the non-coated
photoreceptor 50 in consideration of the above-mentioned fact.
[0102] Additionally, the surface temperature of the non-coated
photoreceptor 50 may be controlled using a method not shown, or a
natural increase in temperature during the discharging may be used.
In the case of when the non-coated photoreceptor 50 is heated, a
heater may be provided out of the non-coated photoreceptor 50 or in
the non-coated photoreceptor. In the case of when the non-coated
photoreceptor 50 is cooled, cooling gas or liquid may circulate in
the non-coated photoreceptor 50.
[0103] In order to avoid an increase in temperature of the
non-coated photoreceptor 50 due to the discharge, it is preferable
to control the flow of gas that comes into contact with the surface
of the non-coated photoreceptor 50 and has high energy. In
connection with this, conditions, such as the flow rate of gas, a
discharge output, and a pressure, may be adjusted to obtain the
desired temperature.
[0104] In the method of generating the plasma using the film
forming apparatus 30 shown in FIG. 4, a high frequency oscillation
device is used, but the device is not limited thereto. For example,
a microwave oscillation device may be used, or an electro-cyclotron
resonance type or helicon plasma type of device may be used.
Furthermore, the high frequency oscillation device may be an
inductance type or a capacitance type.
[0105] In an exemplary embodiment of the present invention, the
plasma generating device includes the discharge electrode 54, the
high frequency electric source 58, the matching box 56, the gas
feeding pipe 34, the MFC 36, the pressure controller 38, and the
gas feeding source 40, and one plasma generating device is used.
However, two or more types of plasma generating devices may be used
in combination, or two or more devices that are the same type may
be used. Additionally, a capacitance combination type of plasma CVD
device where a cylindrical electrode surrounds the cylindrical
non-coated photoreceptor 50 may be used, or a device where the
discharge occurs between the parallel plate electrode and the
non-coated photoreceptor 50 may be used.
[0106] In the case of when two or more plasma generating devices
that are different types are used, it is necessary to
simultaneously form discharges using the same pressure.
Furthermore, a difference in pressure may be formed in a discharge
region and a film-forming region (on which the non-coated
photoreceptor 50 is provided). The devices may be disposed in
series with respect to the gas flow ranging from a gas inlet to a
gas outlet in the treatment device, or the devices may be disposed
so as to face the film-forming surface of the non-coated
photoreceptor 50.
[0107] The discharge may be conducted in the vicinity of the
atmospheric pressure. The term "in the vicinity of the atmospheric
pressure" refers to a pressure of from 70,000 Pa to 110,000 Pa. In
this case, the discharge is readily stabilized through the use of a
rare gas such as He or Ar gas mixed with hydrogen.
[0108] The gas containing the group 13 element may be
triethylgallium in place of trimethylgallium, or other organic
metal compound containing indium or aluminum in place of gallium.
These gases may be used in combination of two or more of them.
[0109] Hydrogen, oxygen, and the group 13 element activated by the
above-described method reside on the photoreceptor, and the
activated hydrogen desorbs hydrogen molecules from the hydrocarbon
group such as a methyl group or an ethyl group composing the
organic metal compound. Accordingly, the surface layer 3 is formed
on the photoreceptor surface, wherein the surface layer 3 is
composed of a hard film containing three-dimensional bonds between
hydrogen, oxygen, and the group 13 element.
[0110] (Conductive Substrate and Photosensitive Layer)
[0111] The photoreceptor in accordance with the exemplary
embodiment has an inorganic photosensitive layer or an organic
photosensitive layer formed on a conductive substrate, and a
surface layer. The photosensitive layer may be of function
separation type wherein a charge generating layer and a charge
transport layer are separated. In the structure of function
separation type, either of the charge generating layer or the
charge transport layer may be arranged on the surface side.
Examples of the inorganic photosensitive layer include amorphous
silicon and amorphous selenium. As necessary, an undercoat layer
may be provided between the conductive substrate and the
photosensitive layer. In addition, as described above, an
intermediate layer such as a cushioning layer may be provided
between the surface layer and the photosensitive layer.
[0112] The conductive base substance includes: a metal drum of for
example aluminum, copper, iron, stainless, zinc, and nickel; a
metal such as aluminum, copper, gold, silver, platinum, palladium,
titanium, nickel-chromium, stainless steel, and copper-indium
deposited on a base material such as a sheet, a paper, a plastic,
and a glass; a conductive metal compound such as indium oxide and
tin oxide deposited on the base material; a metal foil laminated on
the base material; and carbon black, indium oxide, tin
oxide-antimony oxide powder, metal powder, copper iodide, and the
like dispersed into a binder resin and applied on the base material
for conduction treatment. Moreover, the shape of the conductive
base substance may be any one of drum shape, sheet shape, and plate
shape.
[0113] Moreover, if a metal pipe base substance is used as the
conductive base substance, the surface of the metal pipe base
substance may be the original pipe as it is. However, it is also
possible to roughen the surface of the base substance surface by a
surface treatment in advance. Such a surface roughening can prevent
the uneven concentration in the grain form due to the coherent
light which may occur in the photoreceptor if a coherent light
source such as a laser beam is used as an exposure light source.
The method of surface treatment includes specular cutting, etching,
anodization, rough cutting, centerless grinding, sandblast, and wet
honing.
[0114] In particular, from the point of improving the adhesiveness
with the photosensitive layer and improving the film forming
property, one having an anodized surface of the aluminum base
substance may be used as the conductive base substance.
[0115] Hereunder is a description of a method of manufacturing the
conductive substrate having the anodized surface. First, as to the
substrate, pure aluminum or aluminum alloy (for example, aluminum
or aluminum alloy of number between 1000 and 1999, between 3000 and
3999, or between 6000 and 6999 defined in JIS, the disclosure of
which is incorporated by reference) is prepared. Next, anodization
is performed. The anodization is performed in an acid bath of for
example chromic acid, sulfuric acid, oxalic acid, phosphoric acid,
boric acid, and sulfamic acid. Treatment using a sulfuric acid bath
is often used. The anodization is performed for example under a
condition of about sulfuric acid concentration: from 10 weight % to
20 weight %: bath temperature: from 5.degree. C. to 25.degree. C.,
current density: from 1 A/dm.sup.2 to 4 A/dm.sup.2, bath voltage:
from 5V to 30V, and treatment time: 5 minutes to 60 minutes,
however it is not limited to this.
[0116] The anodized film formed on the aluminum substrate in this
manner is porous and highly insulative, and has a very unstable
surface. Therefore, after forming the film, the physical
characteristics value is easily changed over time. In order to
prevent this change of the physical characteristics value, the
anodized film is further sealed. Example of the sealing methods
include a method of soaking the anodized film in an aqueous
solution containing nickel fluoride or nickel acetate, a method of
soaking the anodized film in boiling water, and a method of
treating by steam under pressure. Among these methods, the method
of soaking in an aqueous solution containing nickel acetate is most
often used.
[0117] On the surface of the anodized film that has been sealed in
this manner, metal salts and the like adhered by the sealing remain
in excess. If such metal salts and the like remain in excess on the
anodized film of the substrate, not only the quality of the coating
film formed on the anodized film is badly affected, but also low
resistant components tend to remain in general. Therefore, if this
substrate is used for the photoreceptor to form an image, it
becomes the causative factor of scumming.
[0118] Here, following the sealing, washing of the anodized film is
performed in order to remove the metal salts and the like adhered
by the sealing. The washing may be such that the substrate is
washed once, however it may be such that the substrate is washed by
multisteps of washing. As this time, as the washing solution at the
last washing step, there is used clean (deionized) washing solution
as much as possible. Moreover, in any one step among the multisteps
of washing, a physical rubbing washing using a contact member such
as a brush may be performed.
[0119] The thickness of the anodized film on the surface of the
conductive substrate formed as above is preferable within a range
of 3 .mu.m to 15 .mu.m. On the anodized film is present a layer
called a barrier layer along the porous shaped most outer surface
of a porous anodized film. The thickness of the barrier layer is
preferable in a range from 1 nm to 100 nm in the photoreceptor of
an exemplary embodiment of the present invention. In the above
manner, the anodized conductive substrate 1 can be obtained.
[0120] In the conductive substrate obtained in this manner, the
anodized film formed on the substrate by anodization has a high
carrier blocking property. Therefore, the photoreceptor using this
conductive substrate can be installed in the image forming
apparatus so as to prevent point defects (black dots and scumming)
occurring if print off development (negative/positive development)
is performed, and to prevent current leak phenomenon from a contact
electrification device which often occurs at the time of contact
electrification. Moreover, by sealing the anodized film, the change
of the physical characteristics value over time after forming the
anodized film, may be prevented. Moreover, by washing the
conductive substrate after sealing, the metal salts and the like
adhered on the surface of the conductive substrate by sealing may
be removed. If an image is formed by an image forming apparatus
comprising a photoreceptor produced using this conductive
substrate, it is possible to sufficiently prevent the occurrence of
scumming.
[0121] Regarding the photosensitive layer provided on the
conductive substrate, the overview of a preferable structure having
an amorphous silicon photoreceptor as the photosensitive layer is
given below.
[0122] The amorphous silicon photoreceptor may be for positive
charging or negative charging. The photoreceptor may be made by
forming an undercoat layer on the conductive substrate thereby
preventing charge injection and improving adhesiveness, and then
forming thereon a light conductive layer and a surface layer. The
surface layer may be formed on the surface of an undercoat layer
provided as an intermediate layer on the photosensitive layer, or
directly on the surface of the photosensitive layer.
[0123] The uppermost layer of the photosensitive layer (the layer
on the surface layer side) may be p-type or n-type amorphous
silicon, and an intermediate layer (charge injection inhibiting
layer) such as Si.sub.xO.sub.(1-x): H, Si.sub.xN.sub.(1-x):H,
Si.sub.xC.sub.(1-x):H (0.ltoreq.X.ltoreq.0.99), or an amorphous
carbon layer may be formed between the photosensitive layer and the
surface layer.
[0124] The case where the photosensitive layer is an organic
photoreceptor is further described below. In this case, the
structure is composed mainly of a charge generating layer and a
charge transport layer, and as necessary includes an undercoat
layer and an intermediate layer as described above. Examples of the
material of the under coating layer include: a polymeric resin
compound such as an acetal resin (for example, polyvinyl butyral),
a polyvinylalcohol resin, casein, a polyamide resin, a cellulose
resin, a gelatin, a polyurethane resin, a polyester resin, a
methacrylic resin, an acrylic resin, a polyvinylchloride resin, a
polyvinyl acetate resin, a vinyl chloride-vinyl acetate-maleic
anhydride resin, a silicone resin, a silicone-alkyd resin, a
phenol-formaldehyde resin, and a melamine resin; an organometallic
compound containing zirconium, titanium, aluminum, manganese,
silicon atoms, and the like.
[0125] These compounds may be used solely, or as a mixture or
polycondensate of multiple compounds. Among them, an organometallic
compound containing zirconium or silicon is preferably used since
it has a low residual potential, low potential change due to
environment, and low potential change due to repetitive usage.
Moreover, the organometallic compound may be used solely, or as a
mixture of two or more types, or a mixture with the abovementioned
binder resin.
[0126] Examples of the organic silicon compound (organometallic
compound containing silicon atoms) include vinyltrimethoxysilane,
.gamma.-methacryloxypropyl-tris(.beta.-methoxyethoxy)silane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane, N,
N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane, and
.gamma.-chloropropyltrimethoxysilane. Among them, there is
preferably used a silane coupling agent such as
vinyltriethoxysilane, vinyltris(2-methoxyethoxysilane),
3-methacryloxypropyltrimethoxysilane,
3-glycidoxypropyltrimethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
N-2-(aminoethyl)3-aminopropyltrimethoxysilane,
N-2-(aminoethyl)3-aminopropylmethyldimethoxysilane,
3-aminopropyltriethoxysilane,
N-phenyl-3-aminopropyltrimethoxysilane,
3-mercaptopropyltrimethoxysilane, and
3-chloropropyltrimethoxysilane.
[0127] Examples of the organic zirconium compound (organometallic
compound containing zirconium) include zirconium butoxide, ethyl
zirconium acetoacetate, zirconium triethanolamine, acetylacetonato
zirconium butoxide, ethyl acetoacetate zirconium butoxide,
zirconium acetate, zirconium oxalate, zirconium lactate, zirconium
phosphonate, zirconium octanoate, zirconium naphthenate, zirconium
laurate, zirconium stearate, zirconium isostearate, methacrylate
zirconium butoxide, stearate zirconium butoxide and isostearate
zirconium butoxide.
[0128] Examples of the organic titanium compound (organometallic
compound containing titanium) includes tetraisopropyl titanate,
tetranormalbutyl titanate, butyl titanate dimer,
tetra(2-ethylhexyl)titanate, titanium acetylacetonate, polytitanium
acetylacetonate, titanium octylene glycolate, titanium lactate
ammonium salt, titanium lactate, titanium lactate ethyl ester,
titanium triethanolaminate and polyhydroxytitanium stearate.
[0129] The organic aluminum compound (organometallic compound
containing aluminum) includes aluminum isopropylate,
monobutoxyaluminum diisopropylate, aluminum butyrate,
ethylacetoacetate aluminum diisopropylate and aluminum
tris(ethylacetoacetate).
[0130] Moreover, examples of the solvent used for the under coating
layer forming coating liquid which is for forming the under coating
layer include a publicly known organic solvent for example: an
aromatic hydrocarbon solvent, such as toluene and chlorobenzene; an
aliphatic alcohol solvent, such as methanol, ethanol, n-propanol,
iso-propanol and n-butanol; a ketone solvent such as acetone,
cyclohexanone, and 2-butanone; a halogenated aliphatic hydrocarbon
solvent such as methylene chloride, chloroform, and ethylene
chloride; a cyclic or linear ether solvent such as tetrahydrofuran,
dioxane, ethylene glycol, diethylether; and an ester solvent such
as methyl acetate, ethyl acetate, and n-butyl acetate. These
solvents may be used solely or as a mixture of two or more types.
As a solvent which can be used when two or more types of solvents
are mixed, any solvent may be used as long as a binder resin can be
dissolved therein as a mixed solvent.
[0131] In the formation of the under coating layer, firstly an
under coating layer forming coating liquid that has been formulated
by dispersing and mixing under coating layer coating agent and a
solvent is prepared, and applied on the surface of the conductive
substrate. As the application method of the under coating layer
forming coating liquid, there may be used a normal method such as a
dip coating method, a ring coating method, a wire bar coating
method, a spray coating method, a blade coating method, a knife
coating method, and a curtain coating method. If the under coating
layer is formed, it is preferable to be formed so that the
thickness is in a range from 0.1 .mu.m to 3 .mu.m. By setting the
thickness of the under coating layer within such a thickness range,
potential increase due to desensitization or repetition may be
prevented without overstrengthening the electrical barrier.
[0132] In this manner, by forming the under coating layer on the
conductive substrate, the wettability when coating to form a layer
on the under coating layer may be improved, and it can sufficiently
serve a function as an electrical blocking layer.
[0133] The surface roughness of the under coating layer formed by
the above can be adjusted so as to have a roughness within a range
between 1 and 1/(4n) times the laser wavelength .lamda. for
exposure to be used (where n is the refractive index of a layer
provided on the periphery of the under coating layer). The surface
roughness is adjusted by adding resin particles in the under
coating layer forming coating liquid. By so doing, if the
photoreceptor formed by adjusting the surface roughness of the
under coating layer is used for the image forming apparatus,
interference fringes due to the laser source may be sufficiently
prevented. As the resin particles, there may be used silicone resin
particles, crosslink-type PMMA resin particles, and the like.
Moreover, for adjusting the surface roughness, the surface of the
under coating layer may be ground. As the grinding method, there
may be used buffing, sandblasting, wet honing, grinding treatment,
and the like. In the photoreceptor used for the image forming
apparatus of the configuration of positive electrification, laser
incident beams are absorbed in the vicinity of the most outer
surface of the photoreceptor, and further scattered in the
photosensitive layer. Therefore, it is not so strongly needed to
adjust the surface roughness of the under coating layer.
[0134] It is preferable to add various types of additives to the
coating solution for forming the undercoat layer in order to
improve electric properties, environmental safety, and the quality
of image. Examples of the additives include an electron transport
substance that includes a quinone-based compound, such as
chloranyl, bromoanil, and anthraquinone, a
tetracyanoquinodimethane-based compound, a fluorenone compound,
such as 2,4,7-trinitrofluorenone and
2,4,5,7-tetranitro-9-fluorenone, an oxadiazol-based compound, such
as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole,
2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethyl
aminophenyl)-1,3,4-oxadiazole, a xanthone-based compound, a
thiophene compound, and a diphenoquinone compound, such as
3,3',5,5'-tetra-t-butyldiphenoquinone, an electron transport
pigment, such as polycyclic condensates and azos, and a known
material, such as a zirconium chelate compound, a titanium chelate
compound, an aluminum chelate compound, a titanium alkoxide
compound, an organic titanium compound, and a silane coupling
agent.
[0135] Specific examples of the silane coupling agent used here
include silane coupling agents such as vinyltrimethoxysilane,
7-methacryloxypropyl-tris(.beta.-methoxyethoxy)silane,
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane,
N,N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane,
and .gamma.-chloropropyltrimethoxysilane. However, it is not
limited to these.
[0136] Specific examples of the zirconium chelate compound include
zirconium butoxide, zirconium ethyl acetoacetate, zirconium
triethanolamine, acetylacetonate zirconium butoxide, ethyl
acetoacetatezirconium butoxide, zirconium acetate, zirconium
oxalate, zirconium lactate, zirconium phosphnate, zirconium
octanoate, zirconium naphthenate, zirconium laurate, zirconium
stearate, zirconium isostearate, methacrylate zirconium butoxide,
stearate zirconium butoxide, and isostearate zirconium
butoxide.
[0137] Specific examples of the titanium chelate compound include
tetraisopropyl titanate, tetranormalbutyl titanate, butyl titanate
dimer, tetra(2-ethylhexyl)titanate, titaniumacetylacetonate,
polytitaniumacetylacetonate, titanium octylene glycolate, titanium
lactate ammonium salt, titanium lactate, titanium lactate ethyl
ester, titanium triethanolaminate and polyhydroxytitanium
stearate.
[0138] Specific examples of the aluminum chelate compound include
aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum
butyrate, ethylacetoacetate aluminum diisopropylate and aluminum
tris(ethylacetoacetate). These additives may be used solely, or as
a mixture or polycondensate of multiple compounds.
[0139] Moreover, the abovementioned under coating layer forming
coating liquid may contain at least one type of electron accepting
material. Specific examples of the electron accepting material
include succinic anhydride, maleic anhydride, dibromomaleic
anhydride, phthalic anhydride, tetrabromophthalic anhydride,
tetracyanoethylene, tetracyanoquinodimethane, o-dinitrobenzene,
m-dinitrobenzene, chloranil, dinitroanthraquinone,
trinitrofluorenone, picric acid, o-nitrobenzoic acid,
p-nitrobenzoic acid, and phthalic acid. Among them, there are
particularly preferably used fluorenones, quinines, and benzene
derivatives having an electron attractive substituent such as Cl,
CN, and NO.sub.2. As a result, in the photosensitive layer, the
photosensitivity may be improved, the residual potential may be
decreased, and the deterioration of photosensitivity when used
repeatedly may be reduced. The uneven concentration of the toner
image formed by the image forming apparatus including the
photoreceptor containing an electron accepting material in the
under coating layer may be sufficiently prevented.
[0140] Moreover, a dispersion type under coating layer coating
agent described below is preferable to be used instead of the
abovementioned under coating layer coating agent. As a result, by
appropriately adjusting the resistance of the under coating layer,
residual charge may be prevented from being accumulated, and the
under coating layer may be made thicker. Therefore, the leak
resistance of the photoreceptor may be improved, in particular,
leaking at the time of contact electrification may be
prevented.
[0141] This dispersion type under coating layer coating agent may
be, for example, those obtained by dispersing, in a binder resin,
metal powder such as aluminum, copper, nickel, and silver;
conductive metal oxide such as antimony oxide, indium oxide, tin
oxide, and zinc oxide; and conductive material such as carbon
fiber, carbon black, and graphite powder. As the conductive metal
oxide, metal oxide particles having a mean primary particle size of
0.5 .mu.m or less are preferably used. If the mean primary particle
size is too large, conduction paths are often generated locally,
readily causing current leaking, which may result in the occurrence
of fogging or leaking of large current from the electrification
device. The under coating layer is needed to be adjusted to an
appropriate resistance in order to improve the leak resistance.
Therefore, the abovementioned particles having a mean primary
particle size of 0.5 .mu.m or less are preferable to have a powder
resistance of 10.sup.2 .OMEGA.cm to 10.sup.11 .OMEGA.cm or
less.
[0142] If the resistance of the metal oxide particle is lower than
the lower limit of the above range, sufficient leak resistance may
not be obtained. If it is higher than the upper limit of this
range, the residual potential may be increased. Consequently, among
them, metal oxide particles such as stannic oxide, titanium oxide,
and zinc oxide are preferably used. Moreover, the metal oxide
particles may be used in a mixture of two or more types thereof.
Furthermore, by performing the surface treatment on the metal oxide
particles using a coupling agent, the resistance of the powder may
be controlled. As the coupling agent that may be used in this case,
similar materials as those for the abovementioned under coating
layer forming coating liquid can be used. Moreover, these coupling
agents may be used in a mixture of two or more types thereof
[0143] In this surface treatment of the metal oxide particles, any
publicly known method can be used, and either a dry method or wet
method may be used.
[0144] If a dry method is used, firstly the metal oxide particles
are heated and dried, to remove the surface adsorbed water. By
removing the surface adsorbed water, the coupling agent may be
evenly adsorbed on the surface of the metal oxide particles. Next,
while stirring the metal oxide particles by a mixer or the like
having a large shearing force, the coupling agent, either directly
or dissolved in an organic solvent or water, is dropped or sprayed
with dry air or nitrogen gas, and thereby the treatment is evenly
performed. When the coupling agent is dropped or sprayed, the
treatment may be performed at a temperature of 50.degree. C. or
more. After adding or spraying the coupling agent, printing may be
further performed at a temperature of 100.degree. C. or more. By
the effect of the printing, the coupling agent can be cured and a
firm chemical reaction with the metal oxide particles can be
generated. The printing may be performed at a temperature at which
a desired electrophotographic characteristic is obtained, for any
range of time.
[0145] If a wet method is used, similarly to the dry method,
firstly the surface adsorbed water on the metal oxide particles is
removed. As the method of removing the surface adsorbed water, in
addition to the heat and dry method which is similar to the dry
method, there may be performed a method of removing by stirring and
heating in a solvent used for surface treatment, and a method of
removing by azeotroping with a solvent. Next, the metal oxide
particles are stirred in a solvent, and dispersed by using
ultrasonic waves, a sandmill, an attritor, a ball mill, or the
like. The coupling agent solution is added thereinto, and stirred
or dispersed. Then, the solvent is removed, and thereby the
treatment is evenly performed. After removing the solvent, printing
may be further performed at a temperature of 100.degree. C. or
more. The printing may be performed at a temperature at which a
desired electrophotographic characteristic is obtained, for any
range of time.
[0146] The amount of the surface treatment agent with respect to
the metal oxide particles may be an amount by which a desired
electrophotographic characteristic is obtained. The
electrophotographic characteristic is affected by the amount of the
surface treatment agent adhered on the metal oxide particles after
surface treatment. In the case of the silane coupling agent, the
adhered amount is obtained by the Si intensity measured by
fluorescent X-ray spectroscopy (caused by silane coupling agent),
and the intensity of the main metal element used in the metal
oxide. The Si intensity measured by fluorescent X-ray spectroscopy
may be within a range of from 1.0.times.10.sup.-5 times to
1.0.times.10.sup.-3 times of the intensity of the main metal
element used in the metal oxide. If it is lower than this range,
image defects such as blushing may often occur. If it exceeds this
range, the concentration may be often decreased due to an increase
in the residual potential.
[0147] Examples of the binding resin contained in the dispersion
type under coating layer coating agent include: a publicly known
polymeric resin compound such as an acetal resin (for example,
polyvinyl butyral), a polyvinylalcohol resin, casein, a polyamide
resin, a cellulose resin, a gelatin, a polyurethane resin, a
polyester resin, a methacrylic resin, an acrylic resin, a
polyvinylchloride resin, a polyvinyl acetate resin, a vinyl
chloride-vinyl acetate-maleic anhydride resin, a silicone resin, a
silicone-alkyd resin, a phenol resin, a phenol-formaldehyde resin,
a melamine resin, and an urethane resin; a charge transport resin
having a charge transport group; and a conductive resin such as
polyaniline.
[0148] Among them, there is preferably used a resin that is
insoluble in a coating solvent of a layer formed on the under
coating layer. In particular, a phenol resin, a phenol-formaldehyde
resin, a melamine resin, an urethane resin, an epoxy resin, and the
like are preferably used. The ratio of the metal oxide particles to
the binder resin in the dispersion type under coating layer forming
coating liquid may be arbitrarily set within a range by which a
desired photoreceptor characteristic may be obtained.
[0149] Examples of the method of dispersing the metal oxide
particles that have been surface treated by the above method into
the binder resin, include a method using a media disperser such as
a ball mill, a vibratory ball mill, an attritor, a sandmill, and a
horizontal sandmill, or a medialess disperser such as an agitator,
an ultrasonic disperser, a roll mill, and a high pressure
homogenizer. Furthermore, examples of the high voltage homogenizer
include a collision method where a dispersing liquid is dispersed
by liquid-liquid collision or liquid-wall collision under a high
pressure, and a penetration method where a dispersing liquid is
dispersed by making it penetrate through minute channels under a
high pressure.
[0150] The method of forming the under coating layer by this
dispersion type under coating layer coating agent can be performed
similarly to the method of forming the under coating layer using
the abovementioned under coating layer coating agent.
[0151] Next is a description of the photosensitive layer,
separately for the charge transport layer and the charge generation
layer in this order.
[0152] Examples of the charge transport material used for the
charge transport layer 2B are as follows. That is, there is used a
hole transport material such as: oxadiazoles such as
2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole; pyrazolines such as
1,3,5-triphenyl-pyrazoline, and
1-[pyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminostyryl)pyrazoli-
ne; an aromatic tertiary amino compound such as triphenylamine,
tri(p-methyl)phenylamine,
N,N-bis(3,4-dimethylphenyl)biphenyl-4-amine, dibenzylaniline, and
9,9-dimethyl-N,N-di(p-tolyl)fluorenone-2-amine; an aromatic
tertiary diamino compound such as
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1-biphenyl]-4,4'-diamine;
1,2,4-triazines such as
3-(4'dimethylaminophenyl)-5,6-di-(4'-methoxyphenyl)-1,2,4-triazine;
hydrazones such as
4-diethylaminobenzaldehyde-1,1-diphenylhydrazone,
4-diphenylaminobenzaldehyde-1,1-diphenylhydrazone,
[p-(diethylamino)phenyl](1-naphthyl)phenylhydrazone,
1-pyrenediphenylhydrazone,
9-ethyl-3-[(2methyl-1-indolinylimino)methyl]carbazole,
4-(2-methyl-1-indolinyliminomethyl)triphenylamine,
9-methyl-3-carbazolediphenylhydrazone,
1,1-di-(4,4'-methoxyphenyl)acrylaldehydediphenylhydrazone, and
.beta.,.beta.-bis(methoxyphenyl)vinyldiphenylhydrazone;
quinazolines such as 2-phenyl-4-styryl-quinazoline; benzofurans
such as 6-hydroxy-2,3-di(p-methoxyphenyl)-benzofuran;
.alpha.-stilbenes such as
p-(2,2-diphenylvinyl)-N,N-diphenylaniline; enamines; carbazoles
such as N-ethylcarbazole; poly-N-vinylcarbazole and the derivatives
thereof. Examples thereof further include a polymer having a group
including any of the above compounds on the main chain or side
chain. These charge transport materials may be used solely or in
combination of two or more types thereof.
[0153] Any binder resin may be used as the binder resin used for
the charge transport layer. However, in particular, preferably the
binder resin is compatible with the charge transport material and
has an appropriate strength.
Examples of this binder resin include: various polycarbonate resins
of bisphenol A, bisphenol Z, bisphenol C, bisphenol TP, and the
like, and the copolymer thereof; a polyalylate resin and the
copolymer thereof; a polyester resin; a methacrylic resin; an
acrylic resin; a polyvinylchloride resin; a polyvinylidene chloride
resin; a polystyrene resin; a polyvinyl acetate resin; a
styrene-butadiene copolymer resin; a vinyl chloride-vinyl acetate
copolymer resin; a vinyl chloride-vinyl acetate-maleic anhydride
copolymer resin; a silicone resin; a silicone-alkyd resin; a
phenol-formaldehyde resin; a styrene-acrylic copolymer resin, an
styrene-alkyd resin; a poly-N-vinylcarbazole resin; a polyvinyl
butyral resin; and a polyphenylene ether resin. These resins may be
used solely, or as a mixture of two or more types thereof.
[0154] The molecular weight of the binder resin used for the charge
transport layer is appropriately selected according to the
film-forming condition such as the thickness of the photosensitive
layer 2 and the kind of solvent, and usually it is preferably in
the range from 3,000 to 300,000 and more preferably from 20,000 to
200,000 in the viscosity-average molecular weight.
[0155] The compounding ratio of the charge transport material to
the binder resin is preferable in the range from 10:1 to 1.5.
[0156] The charge transport layer and/or the charge Generation
layer described later may contain additives such as an antioxidant,
a photostabilizer, and a thermal stabilizer, in order to prevent
the deterioration of the photoreceptor due to ozone or oxidizing
gas generated in the image forming apparatus, light, or heat.
[0157] Examples of the antioxidant include hindered phenol,
hindered amine, paraphenylendiamin, arylalkane, hydroquinone,
spirochromans, spiroindanone, or the derivatives thereof, an
organic sulfur compound, and an organophosphorus compound.
[0158] Specific examples of the compound of the antioxidant
include: a phenolic antioxidant such as
2,6-di-t-butyl-4-methylphenol, styrenated phenol,
n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl) -propionate,
2,2'-methylene-bis-(4-methyl-6-t-butylphenol),
2-t-butyl-6-(3'-t-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenylacrylat-
e, 4,4'-butylidene-bis-(3-methyl-6-t-butyl-phenol),
4,4'-thio-bis-(3-methyl-6-t-butylphenol),
1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate,
tetrakis-[methylene-3-(3',5'-di-t-butyl-4'-hydroxy-phenyl)propionate]-met-
hane, and
3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1-
,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane,
3-3',5'-di-t-butyl-4'-hydroxyphenyl)stearyl propionate.
[0159] Examples of the hindered amine compound include
bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,
bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate,
1-[2-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy]ethyl]-4-[3-(3,5-di--
t-butyl-4-hydroxyphenyl)propionyloxy]-2,2,6,6-tetramethylpiperidine,
8-benzyl-7,7,9,9-tetramethyl-3-octyl-1,3,8-triazaspiro[4,5]undecane-2,4-d-
ione, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, succinic acid
dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine
polycondensate,
poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}
{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,3,6,6-tetramethy-
l-4-piperidyl)imino)], 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butyl
malonic acid bis(1,2,2,6,6-pentamethyl-4-piperidyl), and
N,N'-bis(3-aminopropyl)ethylenediamine-2,4-bis[N-butyl-N-(1,2,2,6,6,-pent-
amethyl-4piperidyl)amino]-6-chloro-1,3,5-triazine condensate.
[0160] Examples of the organic sulfur antioxidant include
dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate,
distearyl-3,3'-thiodipropionate,
pentaerythritol-tetrakis-(.beta.-lauryl-thiopropionate),
ditridecyl-3,3'-thiodipropionate, and 2-mercaptobenzimidazole.
[0161] Examples of the organophosphorus antioxidant include
trisnonylphenylphosphate, triphenylphosphate, and
tris(2,4-di-t-butylphenyl)-phosphate.
[0162] The organic sulfur antioxidants and organophosphorus
antioxidants are called a secondary antioxidant, which can increase
the antioxidative effect synergistically when used with a primary
antioxidant such as a phenol or amine.
[0163] Examples of the photostabilizer includes benzophenones,
benzotriazoles, dithiocarbamates, and tetramethylpiperidines.
[0164] Examples of the benzophenone photostabilizer include
2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone,
and 2,2'-di-hydroxy-4-methoxybenzophenone.
[0165] Examples of the benzotriazole photostabilizer includes
2-(-2'-hydroxy-5'methylphenyl-)-benzotriazole,
2-[2'-hydroxy-3'-(3'',4'',5'',6''-tetra-hydrophthalimide-methyl)-5'-methy-
lphenyl]-benzotriazole, 2-(-2'-hydroxy-3'-t-butyl
5'-methylphenyl-)-5-chlorobenzotriazole,
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl-)-5-chloro benzotriazole,
2-(2'-hydroxy-3',5'-t-butylphenyl-)-benzotriazole,
2-(2'-hydroxy-5'-t-octylphenyl)-benzotriazole, and
2-(2'-hydroxy-3',5'-di-t-amylphenyl-)-benzotriazole.
[0166] Examples of other photostabilizers include 2,4,
di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate, and nickel
dibutyl-dithiocarbamate.
[0167] The charge transport layer can be formed by applying and
drying a solvent having the charge transport material and the
binder resin dissolved in an appropriate solvent. Examples of the
solvent used for adjusting the charge transport layer forming
coating liquid include: aromatic hydrocarbons, such as benzene,
toluene, and chlorobenzene; ketones such as acetone and 2-butanone;
halogenated aliphatic hydrocarbons such as methylene chloride,
chloroform, and ethylene chloride; cyclic or linear ethers such as
tetrahydrofuran, dioxane, ethylene glycol, diethylether; and mixed
solvents thereof.
[0168] Moreover, the charge transport layer forming coating liquid
may be added with a small amount of silicone oil as a leveling
agent for improving the smoothness of the coating film formed by
coating.
[0169] The application of the charge transport layer forming
coating liquid can be performed according to the shape and usage of
the photoreceptor, by using a method such as a dip coating method,
a ring coating method, a spray coating method, a bead coating
method, a blade coating method, a roller coating method, a knife
coating method, and a curtain coating method. It is preferable to
be heated and dried after becoming dry to touch at a room
temperature. The heating and drying may be performed in a
temperature range of 30.degree. C. to 200.degree. C., for 5 minutes
to 2 hours.
[0170] The film thickness of the charge transport layer may be
preferably in a range of 5 .mu.m to 50 .mu.m, and more preferably
in a range of 10 .mu.m to 40 .mu.m.
[0171] The charge generation layer may be formed by deposition of a
charge generating material by a vacuum deposition method, or
coating of a solution containing an organic solvent and a binder
resin.
As to the charge generating material, there may be used: amorphous
selenium, crystalline selenium, selenium-tellurium alloy,
selenium-arsenic alloy, and other selenium compounds; an inorganic
photoconductor such as selenium alloy, zinc oxide, and titanium
oxide; or a dye-sensitized material thereof; various phthalocyanine
compound such as metal-free phthalocyanine, titanyl phthalocyanine,
copper phthalocyanine, tin phthalocyanine, and
galliumphthalocyanine; various organic pigments such as
squaryliums, anthanthrones, perylenes, azos, anthraquinones,
pyrenes, pyrylium salt, and thia pyrylium salt; or dyes.
[0172] Moreover, these organic pigments generally have several
types of crystal forms. In particular, for the phthalocyanine
compound, various crystal forms are known such as .alpha. type and
.beta. type. As long as the pigment provides the sensitivity or
other characteristics according to the purpose, any of these
crystal forms can be used.
[0173] Among the abovementioned charge generating materials,
phthalocyanine compounds are preferred. In this case, if light is
irradiated on the photosensitive layer, the phthalocyanine compound
contained in the photosensitive layer absorbs photons and generates
carriers. At this time, since the phthalocyanine compound has a
high quantum efficiency, the absorbed photons can be efficiently
absorbed to generate carriers.
[0174] Furthermore, among the phthalocyanine compound, the
phthalocyanine as shown in the following (1) to (3) are more
preferred. That is:
[0175] (1) Hydroxy gallium phthalocyanine of a crystal form having
diffraction peaks at least in the positions of 7.6.degree.,
10.0.degree., 25.2.degree., and 28.0.degree. in the Bragg angle
(2.theta..+-.0.2.degree.) of an X-ray diffraction spectrum using Cu
k.alpha. rays as a charge generating material.
[0176] (2) Chlorogallium phthalocyanine of a crystal form having
diffraction peaks at least in the positions of 7.3.degree.,
16.5.degree., 25.4.degree., and 28.1.degree. in the Bragg angle
(2.theta..+-.0.2.degree.) of an X-ray diffraction spectrum using Cu
k.alpha. ray as a charge generating material,
[0177] (3) Titanyl phthalocyanine of a crystal form having
diffraction peaks at least in the positions of 9.5.degree.,
24.2.degree., and 27.3.degree. in the Bragg angle
(2.theta..+-.0.2.degree.) of an X-ray diffraction spectrum using Cu
k.alpha. ray as a charge generating material.
[0178] These phthalocyanine compounds have not only high
photosensitivity in particular, but also high stability of the
photosensitivity. Therefore, the photoreceptor having the
photosensitive layer containing any one of these phthalocyanine
compounds is preferably used as a photoreceptor of a color image
forming apparatus which requires high speed image formation and
repetitive reproducibility.
Due to the crystal shape and the measurement method, these peak
intensity and the position may be slightly out from these values.
However, as long as the X-ray diffraction pattern is basically
matched, it can be judged to be the same crystal form.
[0179] Examples of the binder resin used for the charge generation
layer include the following. That is, polycarbonate resins such as
bisphenol A type and bisphenol Z type, and the copolymer thereof; a
polyalylate resin; a polyester resin; a methacrylic resin; an
acrylic resin; a polyvinylchloride resin; a polystyrene resin; a
polyvinyl acetate resin; a styrene-butadiene copolymer resin; a
vinylidene chloride-acrylnitryl copolymer resin; a vinyl
chloride-vinyl acetate-maleic anhydride copolymer resin; a silicone
resin; a silicone-alkyd resin; a phenol-formaldehyde resin;
styrene-alkyd resin; and a poly-N-vinylcarbazole.
[0180] These binder resins may be used solely or in combination of
two or more types thereof. The mixing ratio of the charge
generation material and the binder resin (charge generation
material: binder resin) is desirably within a range between 10:1
and 1:10 by weight ratio. Moreover, generally, the thickness of the
charge generation layer is preferably in a range from 0.01 .mu.m to
5 .mu.m, and more preferably in a range from 0.05 .mu.m to 2.0
.mu.m.
[0181] Moreover, the charge generation layer may contain at least
one type of electron accepting material in order to improve the
sensitivity, decrease the residual potential, and decrease the
fatigue at the time of repetitive usage. Examples of the electron
accepting material used for the charge generation layer include
succinic anhydride, maleic anhydride, dibromomaleic anhydride,
phthalic anhydride, tetrabromophthalic anhydride,
tetracyanoethylene, tetracyanoquinodimethane, o-dinitrobenzene,
m-dinitrobenzene, chloranil, dinitroanthraquinone,
trinitrofluorenone, picric acid, o-nitrobenzoic acid,
p-nitrobenzoic acid, and phthalic acid. Among them, there are
particularly preferred fluorenones, quinines, and benzenes having
an electron attractive substituent such as Cl, CN, and
NO.sub.2.
[0182] As the method of dispersing the charge generating material
into a resin, there may be used a method such as a roll mill, a
ball mill, a vibratory ball mill, an attritor, a dinomill, a
sandmill, and a colloid mill.
[0183] Examples of the solvent of the coating liquid for forming
the charge generation layer include a publicly known organic
solvent for example: an aromatic hydrocarbon solvent, such as
toluene and chlorobenzene; an aliphatic alcohol solvent, such as
methanol, ethanol, n-propanol, iso-propanol and n-butanol; a ketone
solvent such as acetone, cyclohexanone, and 2-butanone; a
halogenated aliphatic hydrocarbon solvent such as methylene
chloride, chloroform, and ethylene chloride; a cyclic or linear
ether solvent such as tetrahydrofuran, dioxane, ethylene glycol,
diethylether; and an ester solvent such as methyl acetate, ethyl
acetate, and n-butyl acetate.
[0184] These solvents may be used solely or as a mixture of two or
more types. If two or more types of solvents are mixed, any solvent
may be used as long as a binder resin can be dissolved therein as a
mixed solvent. However, if the photosensitive layer has a layer
structure where the charge transport layer 2B and the charge
generation layer are formed in this order from the conductive
substrate side, when the charge generation layer is formed using an
application method such as dip coating in which the lower layer is
readily dissolved, a solvent which does not dissolve the lower
layer such as the charge transport layer is desirably used.
Moreover, when the charge generation layer 2A is formed using a
spray coating method or a ring coating method, in which the lower
layer is eroded relatively less, the solvent can be widely
selected.
[0185] As to the intermediate layer, for example when the
photoreceptor surface is electrified by an electrification device,
in order to prevent a situation where the electrification potential
can not be obtained by injecting the electrification charges from
the photoreceptor surface to the conductive substrate of the
photoreceptor serving as the opposed electrode, a charge injection
blocking layer may be formed as required between the surface layer
and the charge generation layer.
As to the material of the charge injection blocking layer, there
may be used the abovementioned silane coupling agent, titanium
coupling agent, organic zirconium compound, and organic titanium
compound, other organometallic compounds, and a widely-used resin
such as polyester, and polyvinyl butyral. The thickness of the
charge injection blocking layer is appropriately set by considering
the film forming property and the carrier blocking property, in a
range from 0.001 .mu.m to 5 .mu.m.
[0186] <Process Cartridge and Image Forming Apparatus>
[0187] Next, process cartridges and image forming apparatuss
including the photoreceptor of the invention are described with
reference to exemplary embodiments thereof.
[0188] As shown in FIG. 5, the image forming apparatus 82 of the
exemplary embodiment of the invention is provided with an
electrophotographic photoreceptor 80 that rotates in a
predetermined direction (the direction D of the arrow in FIG.
5).
[0189] A charging unit 84, an exposing unit 86, a developing unit
88, a transferring unit 89, an erasing unit 81, and a cleaning
member 87 are formed along the rotation direction of the
electrophotographic photoreceptor 80 in the vicinity of the
electrophotographic photoreceptor 80.
[0190] The charging unit 84 electrically charges the surface of the
electrophotographic photoreceptor 80 so that the surface has a
predetermined potential. The exposing unit 86 exposes the surface
of the electrophotographic photoreceptor 80 that is electrically
charged by the charging unit 84 to form an electrostatic latent
image according to image data. The developing unit 88 stores a
developer containing the toner for developing the electrostatic
latent image, and supplies the stored developer to the surface of
the electrophotographic photoreceptor 80 to develop the
electrostatic latent image, thereby forming a toner image.
[0191] The transferring unit 89 transfers the toner image formed on
the electrophotographic photoreceptor 80 while a recording medium
83 is sandwiched between the electrophotographic photoreceptor 80
and the transferring device, thereby transferring the image onto
the recording medium 83. The toner image that is transferred on the
recording medium 83 is fixed to the surface of the recording medium
83 using a fixing unit now shown.
[0192] The erasing unit 81 removes electricity from the substance
that is attached to the surface of the electrophotographic
photoreceptor 80 and electrically charged. The cleaning member 87
is provided to come into contact with the surface of the
electrophotographic photoreceptor 80, and removes the substance
attached to the surface using friction force to the surface of the
electrophotographic photoreceptor 80.
[0193] Additionally, the image forming apparatus 82 of the
exemplary embodiment of the invention may be a tandem apparatus
that is provided with a plurality of electrophotographic
photoreceptors 80 corresponding to the toners of the various
colors. Further, transferring of the toner image onto the recording
medium 83 may be performed using an internal transferring process
where the toner image formed on the surface of the
electrophotographic photoreceptor 80 is transferred onto an
internal transfer body and then onto the recording medium.
[0194] The process cartridge of the exemplary embodiment of the
invention is removably provided with respect to the main body of
the image forming apparatus 89, and is united with at least the
charging unit 84,andat least one selected from the group consisting
of the developing unit 88, the cleaning member 87, and the erasing
unit 81. In the exemplary embodiment of the invention, the cleaning
unit is not particularly limited, however preferably is a cleaning
blade. Usually, a cleaning blade is more damaging and more abrasive
to the photoreceptor surface in comparison with other cleaning
units.
[0195] However, the process cartridge and the image forming
apparatus 82 in accordance with the exemplary embodiment of the
invention are composed of the electrophotographic photoreceptor of
the invention, which suppresses the increase of the residual
potential caused by repeated use in an electrophotographic process
and has a surface layer having sufficient hardness and thickness
for improving the abrasion resistance, so that the occurrence of
scratches and abrasion on the surface of the electrophotographic
photoreceptor are suppressed over a long period of use, which
results in production of favorable images.
EXAMPLES
[0196] Hereunder is a specific description of exemplary embodiments
of the present invention with reference to Examples. However, the
present invention is not limited to these Examples.
Example 1
[0197] (Making of Electrophotographic Photoreceptor)
[0198] --Formation of Undercoat Layer--
[0199] 100 parts by weight of zinc oxide (average particle
diameter: 70 nm, prototype manufactured by Tayca Corporation) are
mixed with 500 parts by weight of toluene under stirring. To the
mixture 1.5 parts by weight of a silane coupling agent (trade name:
KBM603, manufactured by Shin-Etsu Chemical Co., Ltd.) are added and
stirred for 2 hours. Subsequently, toluene is removed by
distillation under reduced pressure, and baking is conducted at
150.degree. C. for 2 hours.
[0200] To a solution prepared by dissolving 60 parts by weight of
zinc oxide which has been subjected to surface treatment in the way
mentioned above, 15 parts by weight of curing agent (blocked
isocyanate, commercial name: Sumidur BL3175, produced by Sumika
Bayer Urethane Co., Ltd.), and 15 parts by weight of butyral resin
(commercial name: S-LEC BM-1, produced by Sekisui Chemical Co.,
Ltd.) in 85 parts by weight of methyl ethyl ketone, 25 parts by
weight of methyl ethyl ketone is mixed to yield a liquid to be
treated.
[0201] Next, using a horizontal media mill disperser (KDL-PILOT
type, DYNO-MILL, produced by Shinmaru Enterprises Corporation),
dispersion treatment is performed in the following procedures. The
cylinder and stirring mill of the disperser are composed of
ceramics including zirconia as the principal component. Into the
cylinder, glass beads 1 mm in diameter (Hi-Bea D20, produced by
Ohara Inc.) are charged in a bulk filling factor 80 volume %,
followed by dispersion treatment in a circulation system at a
peripheral speed of the stirring mill of 8 m/min and a flow rate of
the liquid to be treated of 1000 mL/min. A magnet gear pump is used
for sending the liquid to be treated.
[0202] In the above-mentioned dispersion treatment, a part of the
liquid to be treated is sampled after a specified time elapse, and
the transmittance at the time of film formation is measured. That
is, the liquid to be treated is applied to a glass plate so that it
might have a thickness of 20 .mu.m, and a coating is formed by
performing curing treatment at 150.degree. for 2 hours. Thereafter,
the transmittance at a wavelength of 950 nm is measured using a
spectrophotometer (U-2000, produced by Hitachi, Ltd.). The
dispersion treatment is completed when the transmittance (value at
a coating thickness of 20 .mu.m) exceeded 70%.
[0203] A under coating layer forming coating liquid is prepared by
adding 0.005 parts by weight of dioctyltin dilaurate as a catalyst
and 0.01 parts by weight of silicone oil (commercial name: SH29PA,
produced by Dow Coming Toray Silicone Co., Ltd.) to the dispersion
obtained in the way described above. This coating liquid is applied
by dip coating to an aluminum substrate having a diameter of 84 mm,
a length of 340 mm and a thickness of 1 mm, followed by dry
hardening at 160.degree. C. for 100 minutes. Thus, an under coating
layer having a thickness of 20 .mu.m is formed.
[0204] --Formation of Photosensitive Layer--
[0205] Next, a photosensitive layer is formed on the under coating
layer. A mixture composed of 15 parts by weight of chlorogallium
phthalocyanine of a crystal form having diffraction peaks at least
in the positions of 7.4.degree., 16.6.degree., 25.5.degree., and
28.3.degree. in the Bragg angle (2.theta..+-.0.2.degree.) of an
X-ray diffraction spectrum using Cuk.alpha. ray as a charge
generating material, 10 parts by weight of vinyl chloride-vinyl
acetate copolymer resin (commercial name: VMCH, produced by Nippon
Unicar Co., Ltd.) as a binder resin, and 300 parts by weight of
n-butyl alcohol is subjected to dispersion treatment for 4 hours in
a sand mill using glass beads having a diameter of 1 mm. Thus, a
charge transport layer forming coating liquid is obtained. The
resulting dispersing liquid is applied to the under coating layer
by dip coating and then dried. Thus, a charge generation layer
having a thickness of 0.2 .mu.m is formed.
[0206] Further, a charge transport layer forming coating liquid is
prepared by adding 4 parts by weight of
N,N-diphenyl-N,N'-bis(3-methylphenyl)-[1,1']biphenyl-4,4'-diamine
and 6 parts by weight of bisphenol Z polycarbonate resin (viscosity
average molecular weight: 40000) to 80 parts by weight of
chlorobenzene and dissolving them. This coating liquid is applied
to the charge generation layer and then dried at a temperature of
130.degree. C. for 40 min to form a charge transport layer having a
thickness of 25 .mu.m. Thus, an organic photoreceptor (non-coated
photoreceptor) is obtained.
[0207] --Formation of Surface Layer--
[0208] Subsequently, a surface layer is formed on the non-coated
photoreceptor by plasma CVD. A piece of Si substrate (5 mm.times.10
mm) for making a reference sample is attached to the non-coated
photoreceptor using an adhesive tape, mounted on the plasma CVD
apparatus shown in FIG. 4, and the inside of the vacuum chamber 32
is evacuated to a pressure of 1.times.10.sup.-2 Pa. Subsequently,
200 sccm of hydrogen gas, 5 sccm of He-diluted oxygen (4%), and 5
sccm of hydrogen-diluted trimethyloallium (about 10%) are supplied
to the vacuum chamber 32 through the gas feeding pipe under control
by the mass flow controller 36. Simultaneously, the pressure in the
vacuum chamber 32 is adjusted to 20 Pa by the conductance valve,
the output of a radio wave of 13.56 MHz is adjusted to 80 W by the
high frequency electric source 58 and the matching box 56, and
matching is accomplished by the tuner. Subsequently electricity is
discharged from the discharge electrode 54, wherein the reflection
wave is 0 W. In that state, a film is formed under rotating at 20
rpm for 73 minutes thereby making a photoreceptor having a surface
layer. The hydrogen-diluted trimethylgallium gas is supplied by
bubbling hydrogen carrier gas into trimethylgallium kept at
0.degree. C. The color of the attached thermotape-indicates that
the temperature during film formation is about 40.degree. C. or
less. The obtained photoreceptor is allowed to stand at a
temperature of 20.degree. C. for 24 hours. The thermotape used here
is a sticker for measuring temperature (commercial name: Temp Plate
P/N101, produced by Wahl Co., Ltd).
[0209] --Analysis and Evaluation of Surface Layer--
[0210] A cleaved section of the Si sample is observed by a scanning
electron microscope (SEM); the thickness of the layer is 0.31
.mu.m.
[0211] The composition of the film formed on the Si sample is
analyzed by Rutherford Back Scattering (RBS) and Hydrogen Forward
Scattering (HFS), and it is found that the elemental composition of
gallium, oxygen, and hydrogen are 36 atom %, 44 atom %, and 20 atom
%, respectively (total composition ratio of the three elements:
1.0), and the abundance ratio of oxygen to gallium is 1.22.
[0212] (Evaluation of Electrophotographic Photoreceptor)
[0213] --Potential Characteristics--
[0214] Subsequently, the potential characteristics of the
electrophotographic photoreceptor having the protective layer is
evaluated. In the first place, the surfaces of the non-coated
photoreceptor before the formation of the surface layer and the
photoreceptor having the surface layer are irradiated with exposing
light (light source: semiconductor laser, wavelength: 780 nm,
output: 5 mW) in a scanning manner with the photoreceptors rotated
at 40 rpm under charging to -700 V by a scorotron electrifier.
[0215] Thereafter, the potential of the photoreceptor is examined
by measurement using a surface potentiometer (Model 344,
manufactured by Trek Japan Corporation) and a probe having a
measurement area width of 10 mm (Model 555P-1, manufactured by Trek
Japan Corporation), wherein the probe placed at a distance of 2 mm
from the photoreceptor is mapped by scanning in the direction of
the drum axis and the direction of drum rotation, and the potential
(residual potential) of the photoreceptor is examined. As a result
of this, it is found that the potential of the non-coated
photoreceptor is -20 V, while that of the photoreceptor having the
surface layer is 27 V, which is a potential at a favorable
level.
[0216] Furthermore, charging and exposure under the above-described
conditions are repeated 100 cycles, and then the residual potential
of the non-coated photoreceptor and the photoreceptor having the
surface layer are measured in the same manner as described above;
the residual potential of the non-coated photoreceptor is -22 V,
while that of the photoreceptor having the surface layer is -30
V.
[0217] --Image Characteristics--
[0218] Next, the electrophotographic photoreceptor in which the
protective layer has been formed is installed as a photoreceptor
into a process cartridge for DOCUCENTRE COLAR 500 produced by Fuji
Xerox Co., Ltd. The process cartridge is attached to a DocuCentre
Colar 500 and a print test of forming images (300 dpi, 30% area
coverage) on an A4-sized paper (commercial name: P PAPER, produced
by Fuji Xerox Office Supply Co., Ltd.) is conducted.
[0219] 10,000 sheets are output under the above-described
conditions, and the output image sample of the 10,000th sheet is
evaluated on the image quality on the basis of the following
criteria:
[0220] A. no abnormality detected in image density and dot
reproducibility;
[0221] B: reduced image density, or partial dot missing and
vertical streaks occur at acceptable levels; and
[0222] C: significantly reduced image density or vertical streaks
occur at unacceptable levels.
[0223] All the results are summarized in Table 1.
Example 2
[0224] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the oxygen
supply during the formation of the surface layer is 8.5 sccm and
the film formation time is 65 minutes.
[0225] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 0.29 .mu.m. The
elemental composition is analyzed in the same manner as Example 1,
and it is found that the elemental composition of gallium, oxygen,
and hydrogen are 35 atom %, 48 atom %, and 17 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxyoen to gallium is 1.37.
[0226] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1. The results are
summarized in Table 1.
Examples 3
[0227] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the oxygen
supply during the formation of the surface layer is 20 sccm and the
film formation time is 60 minutes.
[0228] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 0.30 .mu.m. The
elemental composition is analyzed in the same manner as Example 1,
and it is found that the elemental composition of gallium, oxygen,
and hydrogen are 35 atom %, 50 atom %, and 15 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxygen to gallium is 1.43.
[0229] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1. The results are
summarized in Table 1.
Example 4
[0230] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the film
formation time is 30 minutes.
[0231] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 0.1 .mu.m. The elemental
composition is analyzed in the same manner as Example 1, and it is
found that the elemental composition of gallium, oxygen, and
hydrogen are 35 atom %, 50 atom %, and 15 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxygen to gallium is 1.43.
[0232] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1. The results are
summarized in Table 1.
Example 5
[0233] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the film
formation time is 40 minutes.
[0234] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 0.18 .mu.m. The
elemental composition is analyzed in the same manner as Example 1,
and it is found that the elemental composition of gallium, oxygen,
and hydrogen are 36 atom %, 44 atom %, and 20 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxygen to gallium is 1.22.
[0235] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1.
Example 6
[0236] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the film
formation time is 480 minutes.
[0237] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 2.1 .mu.m. The elemental
composition is analyzed in the same manner as Example 1, and it is
found that the elemental composition of gallium, oxygen, and
hydrogen are 36 atom %, 44 atom %, and 20 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxygen to gallium is 1.22.
[0238] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1, however the output
of half tone images is failed. Then, the amount of light of the
exposing laser of DocuCentre Color 500 is increased five times, and
normal half tone images are obtained. On this account, the
characteristics of the image are evaluated under the fivefold
amount of light of the exposing laser. Exposing light for the
evaluation of the potential characteristics is also increased five
times (25 mW). The results are summarized in Table 1.
Example 7
[0239] A cylindrical Al substrate having a thickness of 1 mm is
mounted on a plasma CVD apparatus for cylindrical substrate, and a
charge injection inhibiting layer composed of n-type SiN.sub.0.5
having a thickness of 3 .mu.m, a photosensitive layer composed of
i-type amorphous silicon having a thickness of 20 .mu.m, and a
charge injection inhibiting surface layer composed of p-type
Si.sub.2C having a thickness of 0.5 .mu.m are formed in this order,
whereby a negatively charged amorphous silicon photoreceptor is
obtained. A surface layer is formed on the surface of the
photoreceptor under the same conditions as Example 1 using the same
film forming apparatus as Example 1 which has a structure shown in
FIG. 4, and thus an amorphous silicon photoreceptor having a
surface layer is obtained.
[0240] The amorphous silicon photoreceptor having the surface layer
is evaluated in the same manner as Example 1, except that the
surface potential is changed to -400 V, and the amount of light is
adjusted using a laser having a wavelength of 650 nm.
[0241] The results including the analysis of the surface layer are
summarized in Table 1.
Comparative Example 1
[0242] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that the oxygen
supply during the formation of the surface layer is 3 sccm and the
film formation time is 85 minutes.
[0243] The section of the photoreceptor is observed by SEM in the
same manner as Example 1; the thickness is 0.32 .mu.m. The
elemental composition is analyzed in the same manner as Example 1,
and it is found that the elemental composition of gallium, oxygen,
and hydrogen are 38 atom %, 41 atom %, and 21 atom %, respectively
(total composition ratio of the three elements: 1.0), and the
abundance ratio of oxygen to gallium is 1.08.
[0244] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1; only blurred images
are produced in the evaluation of image characteristics. The
photoreceptor cannot hold an electrostatic latent image, so that
potential and image characteristics cannot be evaluated.
[0245] The results are summarized in Table 1.
Comparative Example 2
[0246] An electrophotographic photoreceptor having a surface layer
is made in the same manner as Example 1, except that 200 sccm of
hydrogen gas, 10 sccm of He-diluted oxygen (4%), and 50 sccm of
nitrogen gas, and 5 sccm of hydrogen-diluted trimethylgallium
(about 10%) are supplied to the vacuum chamber during the formation
of the surface layer, and the film formation time is changed to 60
minutes.
[0247] The section of the photoreceptor is observed by SEM in the
same manner as Example 1, and it is found that the thickness is
0.32 .mu.m. The elemental composition is analyzed in the same
manner as Example 1, and it is found that the elemental composition
of gallium, oxygen, and hydrogen are 33 atom %, 41 atom %, and 20
atom % (total composition ratio of the three elements: 0.94),
respectively, and the abundance ratio of oxygen to gallium is
1.24.
[0248] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1. The results are
summarized in Table 1.
Comparative Example 3
[0249] An electrophotographic photoreceptor is made in the same
manner as Example 1, except that the surface layer is formed as
follows: a non-coated photoreceptor is introduced into a plasma CVD
apparatus shown in FIG. 4, and the inside of the vacuum chamber 32
is evacuated to pressure of 1.times.10.sup.-2 Pa. Subsequently, 500
sccm of hydrogen gas and 500 sccm of nitrogen gas are supplied to
the vacuum chamber 32 through the gas feeding pipe under control by
the mass flow controller 36. Simultaneously, the pressure in the
vacuum chamber 32 is adjusted to 40 Pa by adjusting the conductance
valve, the output of a radio wave of 13.56 MHz is set to 100 W by
the high frequency electric source 58 and the matching box 56, and
matching is accomplished by the tuner. Subsequently electricity is
discharged from the discharge electrode 54, wherein the reflection
wave is 0 W.
[0250] Subsequently, hydrogen-diluted trimethylgallium gas is
introduced from the gas inlet tube 64 via the shower nozzle 64A
such that the amount of trimethylgallium gas is 0.3 sccm. In that
state, a film is formed under rotating at 20 rpm thereby making a
photoreceptor having a surface layer with a thickness of 0.32
.mu.m. The hydrogen-diluted trimethylgallium gas is supplied by
bubbling hydrogen carrier gas into trimethylgallium kept at
0.degree. C. The color of the attached thermotape indicates that
the temperature during film formation is about 35.degree. C. The
thermotape used here is a sticker for measuring temperature
(commercial name: Temp Plate P/N101, produced by Wahl Co.,
Ltd).
[0251] The obtained photoreceptor is allowed to stand at a
temperature of 25.degree. C. and a relative humidity of 50% for 24
hours to naturally oxidize the photoreceptor.
[0252] Concurrently with the film formation on the non-coated
photoreceptor surface, a film is formed on the Si substrate and the
infrared ray absorption spectrum of the oxidized film is measured;
peaks corresponding to Ga--H, Ga--N, and N--H bonds are detected,
indicating that gallium, nitrogen, and hydrogen are contained in
the surface layer.
[0253] The surface of the oxidized film formed on the Si substrate
is measured by XPS (X-ray photoelectron spectroscopy), and it is
found that the film is composed of 60 atom % of oxygen and 40 atom
% of Ga, and contains no nitrogen. It is also found that the
resolution by XPS in the depth direction is about several
nanometers from the outermost surface. The result of infrared
absorption spectrometry on the whole surface layer indicates that
at least the outermost surface of the surface layer is rich in
oxygen and poor in nitrogen, wherein the concentration of oxygen
atoms in the thickness direction of the surface layer decreases
toward the charge transport layer (the concentration of nitrogen
atoms increases toward the charge transport layer).
[0254] The electrophotographic characteristics of the photoreceptor
are evaluated in the same manner as Example 1. The results are
summarized in Table 1.
TABLE-US-00001 TABLE 1 Surface layer Evaluation Total composition
Abundance Variation in ratio of group 13 ratio of oxygen Residual
image quality Thickness element, oxygen, to group 13 Initial
residual potential after (after 10,000 (.mu.m) and hydrogen element
potential (V) repeat (V) sheets) Example 1 0.31 1.0 1.22 -27 -30 A
Example 2 0.29 1.0 1.37 -38 -64 A Example 3 0.30 1.0 1.43 -50 -94 B
(reduced density) Example 4 0.16 1.0 1.43 -45 -71 B (vertical
streaks) Example 5 0.18 1.0 1.22 -27 -28 B (vertical streaks)
Example 6 2.1 1.0 1.22 -45 -49 A Example 7 0.31 1.0 1.22 -30 -32 A
Comparative 0.32 1.0 1.08 Not available Not available Not available
Example 1 Comparative 0.32 0.94 1.24 -54 -144 C (image Example 2
density) Comparative 0.32 1.0 (outermost 1.50 (outermost -56 -150 C
(image Example 3 surface) surface) density)
[0255] As shown in Table 1, in Examples wherein the composition
ratio between gallium, oxygen, and hydrogen in the surface layer is
about 0.95 or more and the ratio between the oxygen and gallium is
from about 1.1 to about 1.5, the increase of the residual potential
is suppressed in spite of the large thickness of the surface layer.
On the other hand, in Comparative Examples wherein the composition
ratio between oxygen and hydrogen and/or the ratio between the
oxygen and gallium in the surface layer is outside the
above-described range, the increase of the residual potential
cannot be suppressed with image quality kept at high level.
[0256] The invention in accordance with the first aspect of the
invention provides an electrophotographic photoreceptor which
prevents the generation of excessive residual potential, which
usually occurs on a photoreceptor having a protective layer
composed of an inorganic material, and achieves both of high
durability and favorable electrical characteristics.
[0257] The invention in accordance with the second aspect of the
invention imparts more sufficient electrical conductivity to the
surface layer, and suppresses the increase of the residual
potential regardless of the increase of the film thickness.
[0258] The invention in accordance with the third aspect of the
invention provides an electrophotographic photoreceptor which
maintains the mechanical strength of the surface layer, and is
capable of forming an electrostatic latent image upon exposure to
an appropriate amount of light.
[0259] The invention in accordance with the fourth aspect of the
invention efficiently provides an electrophotographic photoreceptor
which achieves both of high durability and favorable electrical
characteristics.
[0260] The invention in accordance with the fifth aspect of the
invention efficiently provides an electrophotographic photoreceptor
which achieves both of high durability and favorable electrical
characteristics.
[0261] The invention in accordance with the sixth aspect of the
invention facilitates handling of an electrophotographic
photoreceptor which prevents the generation of excessive residual
potential and achieves both of high durability and favorable
electrical characteristics, and improves the adaptability of the
photoreceptor to image forming apparatus having various
structures.
[0262] The invention in accordance with the seventh aspect of the
invention stably provides high quality images over a long period
without image density unevenness or image density deterioration
[0263] The foregoing description of the exemplary embodiments of
the present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
[0264] All publications, patent applications, and technical
standards mentioned in this specification are herein incorporated
by reference to the same extent as if such individual publication,
patent application, or technical standard was specifically and
individually indicated to be incorporated by reference.
* * * * *